A calculation method for the minimum effective tightening torque of bolted connections

Abstract

The present application provides a method for calculating the minimum effective locking torque of a bolt connection, including: obtaining parameter data when a friction anti-loosening fastener is pre-tightened, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque; according to the thread friction torque, bolt clamping force torque, support friction torque and locking torque, establishing a loosening torque relationship when the friction anti-loosening fastener is not loosened; according to the loosening torque, thread friction torque, bolt clamping force torque and support friction torque, calculating the minimum effective locking torque, and evaluating the anti-loosening performance of the friction anti-loosening fastener under a standard loosening test based on the minimum effective locking torque. The method described in the present application greatly reduces the workload of friction anti-loosening fasteners in the design and evaluation process, and provides users with a better, faster and more convenient method.

Description

Technical Field

[0001] The present application belongs to the technical field of fastener anti-loosening, and in particular to a method for calculating the minimum effective locking torque of a bolt connection. Background Art

[0002] Threaded fasteners are widely used as basic parts in various engineering fields such as aerospace, navigation, rail transportation, etc. With the continuous improvement of equipment performance requirements, the requirements for fastener performance have become more stringent. The harsh working conditions of traditional fasteners in service are prone to reduce the preload force. The main reasons are the loosening of nuts and fatigue fracture of bolts. These common problems directly threaten the service reliability of high-end equipment. Therefore, improving the fastener preload retention performance has always been a research hotspot for scholars at home and abroad.

[0003] There are three commonly used anti-loosening methods for threaded fasteners: permanent anti-loosening, mechanical anti-loosening and friction anti-loosening. Friction anti-loosening is widely used because of its good anti-loosening performance, easy disassembly and assembly, and low cost. Friction anti-loosening is due to a certain amount of interference between the internal and external threads to prevent loosening. The larger the interference, the greater the friction anti-loosening torque, and the better the anti-loosening effect. However, excessive interference will produce additional stress, which has a negative impact on the fatigue resistance of the fastener.

[0004] In order to improve the anti-loosening performance, the industry often uses three forms of permanent anti-loosening, mechanical anti-loosening and friction anti-loosening. Although these methods can effectively inhibit loosening, they increase the difficulty of processing and pre-tightening, and do not improve fatigue resistance, and may even reduce fatigue resistance. In terms of fatigue resistance, high-strength materials and rolling, shot peening, heat treatment and other methods are often used. These methods can improve fatigue resistance but are not closely combined with anti-loosening technology. It is difficult to achieve fatigue resistance-anti-loosening coordination. In addition, the current general fasteners have uneven internal stress distribution, which leads to stress concentration at fixed positions, overwork during use, and fracture concentrated at overworked positions. The material performance is not maximized. In order to avoid accidents, the method of oversized fasteners is currently used, which is also contrary to the lightweight route. Summary of the invention

[0005] In view of this, the present application aims to propose a method for calculating the minimum effective tightening torque of a bolt connection to solve at least one of the above problems.

[0006] To achieve the above purpose, the technical solution of this application is implemented as follows:

[0007] In a first aspect, the present application provides a method for calculating the minimum effective tightening torque of a bolt connection, comprising:

[0008] Acquire parameter data when the friction anti-loosening fastener is pre-tightened, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque;

[0009] According to the thread friction torque, bolt clamping force torque, support friction torque and locking torque, a loosening torque relationship when the friction anti-loosening fastener is not loosened is established;

[0010] The minimum effective locking torque is calculated according to the loosening torque, thread friction torque, bolt clamping force torque and support friction torque, and the anti-loosening performance of the friction anti-loosening fastener under the standard loosening test is evaluated based on the minimum effective locking torque.

[0011] In a second aspect, based on the same inventive concept, the present application further provides a system for calculating the minimum effective tightening torque of a bolt connection, applying the method described in the first aspect, including:

[0012] An acquisition module is configured to acquire parameter data when the friction anti-loosening fastener is pre-tightened, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque;

[0013] An establishing module is configured to establish a loosening torque relationship when the friction anti-loosening fastener is not loosened according to the thread friction torque, the bolt clamping force torque, the support friction torque and the locking torque;

[0014] The calculation module calculates a minimum effective locking torque according to the loosening torque, the thread friction torque, the bolt clamping force torque and the support friction torque, and evaluates the anti-loosening performance of the friction anti-loosening fastener under a standard loosening test based on the minimum effective locking torque.

[0015] Compared with the prior art, the method for calculating the minimum effective tightening torque of a bolt connection described in this application has the following beneficial effects:

[0016] The method for calculating the minimum effective locking torque of a bolt connection described in the present application calculates the minimum effective locking torque of a friction anti-loosening fastener, which greatly reduces the workload of friction anti-loosening fasteners in the design and evaluation process, and provides users with a better, faster and more convenient method. At the same time, this method is combined with new materials, structural optimization, rolling, shot peening, heat treatment and other methods to effectively improve the performance of fasteners on the basis of existing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0018] Figure 1This is a flow chart of a method for calculating the minimum effective locking torque of a bolt connection according to an embodiment of the present application;

[0019] Figure 2 A relationship diagram between the preload torque and the preload force described in the embodiment of the present application;

[0020] Figure 3 Schematic diagram of the preload torque, thread friction torque, bolt clamping torque and support friction torque described in the embodiment of the present application;

[0021] Figure 4 Schematic diagram of the loosening torque, thread friction torque, bolt clamping torque, support friction torque and locking torque described in the embodiment of the present application;

[0022] Figure 5 A schematic diagram of the friction force of the supporting surface of the friction anti-loosening fastener described in an embodiment of the present application;

[0023] Figure 6 This is a schematic diagram of the radial force of the M12 closed nut and bolt described in the embodiment of the present application;

[0024] Figure 7 It is a preload force curve diagram of the common fastener and the friction anti-loosening fastener described in the embodiment of the present application;

[0025] Figure 8 A relationship diagram of the ratio of the pre-tightening torque and the pre-tightening force loss of the friction anti-loosening fastener described in the embodiment of the present application;

[0026] Fig. 9 A relationship diagram between the pre-tightening torque and the minimum effective locking torque of a common fastener described in an embodiment of the present application;

[0027] Fig.10 This is a schematic diagram of the structure of a system for calculating the minimum effective locking torque of a bolt connection described in an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0029] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should be the usual meanings understood by people with ordinary skills in the field to which the present application belongs. The "first", "second" and similar words used in the embodiments of the present application do not represent any order, quantity or importance, but are only used to distinguish different components. "Including" or "comprising" and similar words mean that the elements or objects appearing in front of the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0030] There are two types of friction anti-loosening torque, one is called Prevailing Torque (preset torque), referred to as T P ; The other is called Loose Resistance Torque (loose resistance torque, i.e. locking torque), referred to as T P It is a method for preliminary evaluation of threaded fasteners. It only uses a torque wrench to measure the torque when the nut is screwed into the bolt. No pre-tightening is required. However, for some types of threaded fasteners, T P During the preload process, the phenomenon of reduction may occur, resulting in T P Therefore, this embodiment specifically studies another value of the friction anti-loosening torque. It can be considered as T during the loosening process P , which directly prevents the fastener from loosening when it is loosened. Figure 2 The figure shows the relationship between the preload torque and preload force of common fasteners and some friction-locking threaded fasteners during the preload-loosening process. The black line in the figure represents common fasteners, and the gray line represents friction-locking fasteners. When preloaded to the same preload force, friction-locking fasteners require a larger torque than common fasteners. The extra torque during the preload process is T P , which is represented by the right area in the figure; the extra part during the loosening process is The left part of the diagram indicates the loosening resistance torque at the starting point of loosening. It directly determines whether the fasteners will loosen, so it receives special attention.

[0031] It is the minimum effective tightening torque value that can ensure that friction-locking threaded fasteners do not loosen under standard lateral vibration loosening test conditions (Junker test DIN25201-4). It can quickly evaluate whether the fastener has good anti-loosening performance under the DIN25201-4 standard. It can be obtained by calculating the basic parameters of the fastener.

[0032] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0033] See also Figure 1 As shown, this embodiment provides a method for calculating the minimum effective tightening torque of a bolt connection, which specifically includes the following steps:

[0034] Step S101, obtaining parameter data of a friction anti-loosening fastener during pre-tightening, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque.

[0035] Specifically, in this embodiment, when the friction locking fastener is pre-tightened, as Figure 3 As shown, the preload torque T is the thread friction torque T Thread , Bolt clamping force torque T Axial and support friction torque T Bearing The sum of the three moments, of which only the bolt clamping force moment T Axial is converted into a preload force F, and the other two are consumed to overcome friction. These torques can be calculated using formulas (1)-(5), where d 2 represents the effective diameter of the screw, P represents the pitch, d w It represents the equivalent diameter of the support surface friction and β represents the half angle of the thread.

[0036] T=T Thread +T Azial +T Bearing ⑴

[0037]

[0038]

[0039] Step S102: establishing a loosening torque relationship when the friction anti-loosening fastener is not loosened according to the thread friction torque, the bolt clamping force torque, the support friction torque and the locking torque.

[0040] Specifically, in this embodiment, during the loosening process of the common fastener, the loosening torque T u The friction force generated by the support surface needs to overcome two anti-loosening moments. The preload force T is released in this process. Under the condition of a certain preload force F, T Thread-T Axial +T Bearing is a constant value. u >T Threa -T Axial +T Bearing When the ordinary fastener is loosened.

[0041] If a friction-locking fastener is used instead, the locking torque between the internal and external threads when loosening It will also prevent the fasteners from loosening, which may cause So that the fastener cannot be loosened, such as Figure 4 As shown. Then, the loosening torque T of a fastener with good anti-loosening performance is u It can be expressed by formula (6):

[0042]

[0043] Step S103, calculating the minimum effective locking torque according to the loosening torque, the thread friction torque, the bolt clamping force torque and the support friction torque, and evaluating the anti-loosening performance of the friction anti-loosening fastener under the standard loosening test based on the minimum effective locking torque.

[0044] Specifically, in this embodiment, during the manual loosening process, the loosening torque T u Provided by the wrench, but in the standard loosening test DIN25201-4, the loosening torque T u Provided by the tangential force generated by the vibration testing machine, when the amplitude is constant, the maximum loosening torque T provided by the testing machine u is a fixed value. Under this condition, the locking torque that ensures that the fastener does not loosen is the minimum effective locking torque. With T u The relationship can be expressed by formula (7).

[0045]

[0046] When the friction locking fastener is loosened by tangential force, the loosening torque T u The friction force F of the supporting surface s Caused by F s The preload force F and the friction coefficient μ of the supporting surface w The relationship is calculated by formula (8). s It is not applied uniformly to the entire support surface, so the center of the resultant force P cannot be determined. Figure 5 As shown, the position of the resultant force is represented as P. There is a relative rotation center O between the nut and the bolt. Due to the gap between the bolt and nut threads, the exact position of point O cannot be obtained. After research, it is known that point P and point O are not the same point. There is a distance d between the two. l , dl It is called the loosening radius, and its size is approximately equal to the effective diameter d of the bolt, so d l can be replaced by d. So we can get formula (9), d l is defined as the loose radius.

[0047] F s =F·μ w ⑻

[0048] T u =F s ·d l ⑼

[0049] According to formulas (7)-(9), the minimum locking torque can be derived: The calculation equation of is shown in formula (10). This equation replaces a large number of time-consuming and labor-intensive experiments and can be used in the evaluation of existing friction anti-loosening fasteners and the design of new friction anti-loosening fasteners. It can avoid stress concentration while ensuring the anti-loosening performance of threaded fasteners and improve their fatigue performance.

[0050]

[0051] Therefore, the method described in this embodiment can be used to develop fasteners, and the anti-loosening performance can be maximized while avoiding the reduction of fatigue resistance as much as possible. The torque calculation method is suitable for friction-proof threaded fasteners and closing nuts that generate anti-loosening torque due to radial force.

[0052] The method for calculating the minimum effective locking torque of a bolt connection described in this embodiment calculates the minimum effective locking torque of a friction anti-loosening fastener, which greatly reduces the workload of friction anti-loosening fasteners in the design and evaluation process, and provides users with a better, faster and more convenient method. At the same time, this method is combined with new materials, structural optimization, rolling, shot peening, heat treatment and other methods to effectively improve the performance of fasteners on the basis of existing performance.

[0053] Based on the above method, this application verifies the friction anti-loosening fasteners and ordinary (threaded) fasteners respectively, as follows:

[0054] 1) Friction-proof fasteners

[0055] In this embodiment, an M12 closing nut and an M12 bolt are used to generate anti-loosening torque by radial force, such as Figure 6 As shown in the figure. When the bolt is pre-tightened, the first circle of thread radially squeezes the bolt to produce an interference fit. When the interference Δ increases, the corresponding loosening resistance torque Under the DIN25201-4 standard, different The anti-loosening performance corresponding to the value is as follows Figure 7 As shown, loosening resistance torque The anti-loosening performance of 6.5Nm anti-loosening fasteners is better than that of ordinary fasteners, but there is a greater loss in tightening force F. The preload F value of the fastener is the same as that of 10.2Nm, and both have strong anti-loosening performance. In order to maximize the anti-loosening performance while avoiding the reduction of fatigue resistance as much as possible, it is necessary to determine the optimal balance between the anti-loosening performance of the fastener and the material life. Therefore, the loosening resistance torque is studied. The loss of preload F in fasteners with values ​​between 8.2 Nm and 10.2 Nm. The loss of preload F is defined as the residual preload F residual With initial preload F initial The percentage of residual / F initial％ ).

[0056] like Figure 8 As shown in the figure, due to the initial drop of threaded fasteners, the preload loss ratio cannot reach 100%. residual / F initial％ The larger the value, the better the anti-loosening performance. residual / F initial％ Values ​​as loosening resistance torque In M12 fasteners, when the loosening resistance torque When greater than 8.2Nm, F residual / F initial％ Therefore, the minimum effective anti-loosening torque of M12 fasteners is obtained through experiments.

[0057] 2) Ordinary fasteners

[0058] According to formula (7), loosening experiments and finite element analysis were performed on M12 common fasteners under the DIN25201-4 standard. When loosening begins, an external torque is applied to the nut, and the loosening angle (-θ) of the nut in the loosening experiment is forced to be limited to 0. The applied external torque can be regarded as the The experimental results are as follows Fig. 9 As shown in the figure, under the condition of ensuring that ordinary fasteners do not loosen, the minimum external torque required to be applied is 7.8Nm, that is, the minimum effective loosening resistance torque

[0059] The above examples show that the finite element analysis results of M12 anti-loosening fasteners (8.2Nm) and ordinary fasteners (7.8Nm) are The values ​​are very similar, therefore, the feasibility of the method described in this embodiment is verified.

[0060] It should be noted that the above describes some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the above embodiments and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0061] Based on the same inventive concept, corresponding to any of the above-mentioned embodiments and methods, an embodiment of the present application further provides a system for calculating the minimum effective tightening torque of a bolt connection.

[0062] like Fig.10 As shown, the bolt connection minimum effective tightening torque calculation system, using the method described in the above embodiment, includes:

[0063] An acquisition module 11 is configured to acquire parameter data when the friction anti-loosening fastener is pre-tightened, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque;

[0064] An establishing module 12 is configured to establish a loosening torque relationship when the friction anti-loosening fastener is not loosened according to the thread friction torque, the bolt clamping force torque, the support friction torque and the locking torque;

[0065] The calculation module 13 calculates the minimum effective locking torque according to the loosening torque, the thread friction torque, the bolt clamping force torque and the support friction torque, and evaluates the anti-loosening performance of the friction anti-loosening fastener under the standard loosening test based on the minimum effective locking torque.

[0066] For the convenience of description, the above system is described by dividing the functions into various modules. Of course, when implementing the embodiments of the present application, the functions of each module can be implemented in the same or multiple software and / or hardware.

[0067] The system of the above embodiment is used to implement the corresponding method in any of the above embodiments, and has the beneficial effects of the corresponding method embodiment, which will not be repeated here.

[0068] The embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the scope of protection of the present application.

Claims

1. A method for calculating the minimum effective tightening torque of a bolt connection, characterized in that: include: Acquire parameter data when the friction anti-loosening fastener is pre-tightened, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque; According to the thread friction torque, bolt clamping force torque, support friction torque and locking torque, a loosening torque relationship when the friction anti-loosening fastener is not loosened is established; The minimum effective locking torque is calculated according to the loosening torque, thread friction torque, bolt clamping force torque and support friction torque, and the anti-loosening performance of the friction anti-loosening fastener under the standard loosening test is evaluated based on the minimum effective locking torque; The thread friction torque, bolt clamping torque and support friction torque formulas are respectively expressed as: In the formula, d2 represents the effective diameter of the screw, P represents the pitch, and d w represents the equivalent diameter of the support surface friction, β represents the half angle of the thread, F represents the preload, T Thr Indicates the thread friction torque, T Axial Indicates the bolt clamping force torque, T Bearing represents the support friction torque; The loosening torque relationship formula for establishing the friction anti-loosening fastener when it is not loosened includes: In response to the friction anti-loosening fastener being loosened, the locking torque between the internal and external threads prevents the fastener from loosening, and the loosening torque of the anti-loosening fastener satisfies the following relationship: Where, T Thread Indicates the thread friction torque, T Axial Indicates the bolt clamping force torque, T Bearing represents the support friction torque, Indicates the locking torque, T u Indicates the loosening torque; The loosening torque is calculated by the preload force, the friction coefficient of the support surface and the loosening radius, and the calculation formula is as follows: F s =F·μ w ; T u =F s ·d l ; In the formula, F represents the preload force, μ w represents the friction coefficient of the supporting surface, d l It represents the loosening radius, wherein the loosening radius is obtained from the effective diameter of the bolt.

2. The method according to claim 1, characterized in that: In the standard loosening test, the loosening torque is provided by the tangential force generated by the vibration tester. The maximum loosening torque provided by the tester is a fixed value to ensure that the locking torque when the fastener just does not loosen is the minimum effective locking torque. The relationship between the minimum effective locking torque and the loosening torque is expressed as:

3. The method according to claim 2, characterized in that The minimum effective locking torque formula is expressed as:

4. A system for calculating the minimum effective tightening torque of a bolt connection, using the method according to any one of claims 1 to 3, characterized in that: include: An acquisition module is configured to acquire parameter data when the friction anti-loosening fastener is pre-tightened, wherein the parameter data includes thread friction torque, bolt clamping force torque and support friction torque; An establishing module is configured to establish a loosening torque relationship when the friction anti-loosening fastener is not loosened according to the thread friction torque, the bolt clamping force torque, the support friction torque and the locking torque; The calculation module calculates a minimum effective locking torque according to the loosening torque, the thread friction torque, the bolt clamping force torque and the support friction torque, and evaluates the anti-loosening performance of the friction anti-loosening fastener under a standard loosening test based on the minimum effective locking torque.

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