Internal thread and threaded connection pair

Abstract

The invention provides an internal thread and a threaded connection pair, and belongs to the technical field of threaded connection. The internal thread is a meter-made thread or an MJ thread, a thread profile line of the internal thread comprises a thread top, a straight line section, a thread bottom and a straight line section which are connected in sequence, the thread angle of the internal thread is 60 degrees, the thread pitch is P, the width of the thread top is defined as Cn, the width of the thread bottom is defined as Cn2, the thread height is defined as hn, Cn is larger than 0 and smaller than C0, # imgabs0 #, and C0 is the width of the thread top of the standard meter-made internal thread or the MJ internal thread. The tooth thickness of the internal thread teeth is reduced, the rigidity of the internal thread teeth can be reduced, the bending deflection of the internal thread teeth can be improved, and therefore when the thread connection pair bears alternating loads, the internal thread teeth can generate larger bending deformation to absorb inertia force generated by the alternating loads, and therefore the thread connection pair can bear the alternating loads. Therefore, the stress of the root of the external thread under the action of the alternating load is reduced, and the fatigue performance of the external thread is improved.

Description

Technical Field

[0001] The invention relates to an internal thread and a threaded connection pair, belonging to the technical field of threaded connection. Background Art

[0002] In the field of engineering, thread fatigue fracture is a particularly critical technical challenge, especially in equipment and components that are subjected to high stress and long service life, and its impact cannot be ignored. As a common connection method, thread has been widely used in many industries such as automobiles, aerospace, petrochemicals, and construction. The strength and stability of the connection are directly related to the safety and reliability of the entire structure.

[0003] Among the common threaded connections, there are metric threads and MJ threads. The tooth profiles of standard metric threads are as follows: Figure 1 As shown in the figure, the tooth profile of the internal and external threads includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence, where D is the major diameter of the internal thread, d is the major diameter of the external thread, and D 2 is the middle diameter of the internal thread, d 2 D is the middle diameter of the external thread 1 is the internal thread diameter, d 1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. The crest width of the internal thread is The tooth bottom width is The crest width of the external thread is The tooth bottom width is Since the tooth angle of the internal and external threads is 60°, the tooth height of the internal and external threads can be obtained through geometric calculation. (Right now Figure 1 In ).

[0004] The tooth profile of standard MJ thread is as follows Figure 2 As shown in the figure, the tooth profiles of internal and external threads also include the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence, where D is the major diameter of the internal thread, d is the major diameter of the external thread, and D 2 is the middle diameter of the internal thread, d 2 D is the middle diameter of the external thread 1 is the internal thread diameter, d 1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. Unlike metric threads, the crest width of the MJ internal thread is The tooth bottom width is The crest width of the MJ external thread is The tooth bottom width is Since the tooth angles of the MJ internal and external threads are both 60°, the tooth heights of the MJ internal and external threads can be obtained through geometric calculations as follows: (Right now Figure 2 In ).

[0005] At present, no matter it is metric thread or MJ thread, due to the influence of the thread structure itself, the average thickness of the external thread teeth is smaller than the average thickness of the internal thread teeth, so the stiffness of the internal thread teeth is greater than the stiffness of the external thread teeth, resulting in the threaded connection pair being subjected to alternating loads. The external thread with smaller thread stiffness acts as an energy absorption box for the internal thread with larger stiffness. The external thread teeth will produce greater deformation to share more inertia force, thereby aggravating the stress concentration phenomenon at the bottom of the external thread teeth, resulting in poor fatigue performance of the external thread, and then causing the entities where the external thread is located, such as bolts, studs and other parts, to easily produce fatigue fracture, seriously affecting the safety and reliability of engineering equipment. Summary of the invention

[0006] The purpose of the present invention is to provide an internal thread to solve the problem in the prior art that the stiffness of the internal thread teeth is greater than the stiffness of the external thread teeth, resulting in poor fatigue performance of the external thread when the threaded connection pair is subjected to alternating loads, which in turn causes parts such as bolts and studs to easily suffer fatigue fractures, seriously affecting the safety and reliability of engineering equipment; the purpose of the present invention is also to provide a threaded connection pair to solve the above-mentioned problem.

[0007] To achieve the above purpose, the internal thread in the present invention adopts the following technical solution:

[0008] An internal thread, which is a metric thread or an MJ thread, and the tooth profile of the internal thread includes a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the tooth profile angle of the internal thread is 60°, the pitch is P, and the tooth top width is defined as C n , the tooth bottom width is C n2 , tooth height is h n , 0<C n <C 0 , Among them C 0 It is the crest width of standard metric internal thread or MJ internal thread.

[0009] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which can improve the internal thread crest width C n Further restrictions are made and the tooth bottom width C is given n2 With pitch P and crest width C n The relationship between n <C 0 , Among them C 0 is the crest width of the standard metric internal thread or MJ internal thread. In this way, while keeping the tooth angle at 60°, the crest width C of the internal thread of the present invention is n Compared with the crest width C of standard metric internal thread or MJ internal thread0 To be small, and the tooth bottom width C n2 With crest width C n A certain geometric relationship is maintained between them, so the tooth thickness of the internal thread is at least thinned, which can reduce the rigidity of the internal thread teeth and increase the bending deflection of the internal thread teeth. Further, when the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external thread teeth under the action of the alternating loads, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0010] Further, where h 0 It is the tooth height of standard metric internal thread or MJ internal thread.

[0011] Furthermore, the internal thread is a metric internal thread used in conjunction with a standard metric external thread. According to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0012] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the standard metric external thread are simplified is not greater than 0.36 times the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread are simplified, it is concluded that

[0013]

[0014] Further, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than one-fourth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0015]

[0016] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0017]

[0018] Furthermore, the internal thread is an MJ internal thread used in conjunction with a standard MJ external thread. According to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard MJ external thread is not greater than the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0019] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ external thread are simplified is not greater than 0.55 times the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread are simplified, it is concluded that

[0020]

[0021] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ external thread are simplified is not greater than 0.4 times the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread are simplified, it is concluded that

[0022]

[0023] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard MJ external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0024]

[0025] Furthermore, the internal thread is a metric internal thread for use with a standard metric external thread. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C n ≤0.125P.

[0026] Furthermore, the internal thread is an MJ internal thread for use with a standard MJ external thread. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C n ≤0.125P.

[0027] To achieve the above purpose, the threaded connection pair in the present invention adopts the following technical solution:

[0028] A threaded connection pair, comprising an internal thread and an external thread used in conjunction with the internal thread, wherein the external thread is a standard metric thread or MJ thread, the internal thread is an improved metric thread or MJ thread, and the tooth profile of the internal thread comprises a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the tooth profile angle of the internal thread is 60°, the pitch is P, and the tooth top width is defined as C n , the tooth bottom width is C n2 , tooth height is h n , 0<C n <C 0 , Among them C 0 It is the crest width of standard metric internal thread or MJ internal thread.

[0029] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which can improve the internal thread crest width C n Further restrictions are made and the tooth bottom width C is given n2 With pitch P and crest width C n The relationship between n <C 0 , Among them C 0 is the crest width of the standard metric internal thread or MJ internal thread. In this way, while keeping the tooth angle at 60°, the crest width C of the internal thread of the present invention is n Compared with the crest width C of standard metric internal thread or MJ internal thread 0 To be small, and the tooth bottom width C n2 With crest width C n A certain geometric relationship is maintained between them, so the tooth thickness of the internal thread is at least thinned, which can reduce the rigidity of the internal thread teeth and increase the bending deflection of the internal thread teeth. Further, when the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external thread teeth under the action of the alternating loads, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0030] Further, where h 0 It is the tooth height of standard metric internal thread or MJ internal thread.

[0031] Furthermore, the internal thread is a metric internal thread used in conjunction with a standard metric external thread. According to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0032] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the standard metric external thread are simplified is not greater than 0.36 times the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread are simplified, it is concluded that

[0033]

[0034] Further, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than one-fourth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0035]

[0036] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0037]

[0038] Furthermore, the internal thread is an MJ internal thread used in conjunction with a standard MJ external thread. According to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard MJ external thread is not greater than the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0039] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ external thread are simplified is not greater than 0.55 times the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread are simplified, it is concluded that

[0040]

[0041] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam after the thread teeth of the standard MJ external thread are simplified is not greater than 0.4 times the bending deflection of the rectangular cantilever beam after the thread teeth of the internal thread are simplified, it is concluded that

[0042]

[0043] Furthermore, according to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard MJ external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that

[0044]

[0045] Furthermore, the internal thread is a metric internal thread for use with a standard metric external thread. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C n ≤0.125P.

[0046] Furthermore, the internal thread is an MJ internal thread for use with a standard MJ external thread. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C n ≤0.125P. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a tooth profile diagram of a standard metric thread in the prior art;

[0048] Figure 2 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0049] Figure 3 The figure is a tooth profile diagram of the internal thread embodiment 1 of the present invention;

[0050] Figure 4 It is a schematic diagram of the thread profile of the internal thread embodiment 1 of the present invention being simplified into a cantilever beam;

[0051] Figure 5 This is a thread marking position diagram in internal thread embodiment 1 of the present invention;

[0052] Figure 6 This is a curve diagram showing the change of average stress at a calibrated position over time under the action of an alternating load in Example 1 of the internal thread of the present invention;

[0053] Figure 7 This is a tooth profile diagram of internal thread embodiment 2 of the present invention;

[0054] Figure 8 It is a schematic diagram of the thread profile of the internal thread embodiment 2 of the present invention being simplified into a cantilever beam;

[0055] Fig. 9 In the embodiment 2 of the internal thread of the present invention, k changes with C n and h n Surface graph of the change of

[0056] Fig.10 This is a curve diagram showing the change of the average stress at the calibrated position over time under the action of the alternating load in the internal thread embodiment 2 of the present invention;

[0057] Fig.11 The figure is a tooth profile diagram of the internal thread embodiment 3 of the present invention;

[0058] Fig.12 It is a schematic diagram of the internal thread embodiment 3 of the present invention in which the thread profile is simplified into a cantilever beam;

[0059] Fig.13 This is a curve diagram showing the change of the average stress at the calibrated position over time under the action of the alternating load in the internal thread embodiment 3 of the present invention;

[0060] Fig.14 The figure is a tooth profile diagram of the internal thread embodiment 4 of the present invention;

[0061] Fig.15 It is a schematic diagram of the thread profile of the internal thread embodiment 4 of the present invention being simplified into a cantilever beam;

[0062] Fig.16 In the embodiment 4 of the internal thread of the present invention, k changes with C n and h n Surface graph of the change of

[0063] Fig.17 This is a curve diagram of the average stress at the calibrated position changing with time under the action of alternating load in Example 4 of the internal thread of the present invention. DETAILED DESCRIPTION

[0064] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0065] Embodiment 1 of the internal thread of the present invention:

[0066] The inventive concept of this embodiment is to reduce the tooth thickness of the internal thread teeth, reduce the rigidity of the internal thread teeth, and increase the bending deflection of the internal thread teeth. Then, when the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread.

[0067] Specifically, the internal thread in this embodiment is an improved metric internal thread for use with a standard metric external thread, and the tooth profile of the internal thread in this embodiment is evolved from the tooth profile of the standard metric internal thread, such as Figure 3 As shown, the tooth profile of the internal thread (solid line in the figure) includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The tooth profile angle α of the internal thread is 60°, the pitch is P, the major diameter is D, and the middle diameter is D 2 , the path is D 1 , tooth height is h n , these parameters are the same as those of the standard metric internal thread, so according to the geometric relationship, we can find

[0068] The difference between the internal thread of this embodiment and the standard metric internal thread is that the tooth thickness of the internal thread of this embodiment is thinner, and the crest width of the internal thread of this embodiment is defined as C n , the tooth bottom width is C n2 The crest width of the standard metric internal thread is C 0 According to existing knowledge, Therefore, the crest width C of the internal thread in this embodiment is n Satisfy 0<C n <C 0 , after simplification, we can get 0<C n <0.25P. In addition, according to the geometric relationship, we can find In this way, while keeping the tooth profile angle at 60°, the crest width C of the internal thread of the present invention is n Compared to the crest width C of standard metric internal threads 0 To be small, and the tooth bottom width C n2 Root width compared to standard metric internal threads To be larger, and the tooth bottom width C n2 With crest width C nA certain geometric relationship is maintained between them, which is equivalent to translating the straight line segment on one side of the tooth profile line. In this way, the rigidity of the internal thread teeth can be reduced by thinning the tooth thickness of the internal thread teeth, and the bending deflection of the internal thread teeth can be increased. Then, when the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external thread teeth under the action of the alternating loads, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0069] In order to further explore the crest width C n A better upper limit value is convenient for subsequent analysis, such as Figure 4 As shown, in this embodiment, the threads of the internal thread and the standard metric external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0070] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0071]

[0072] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0073] Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0074] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0075] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0076] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0077] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0078]

[0079] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as:

[0080]

[0081] In the obtained k about C n In the equation, when 0<C n <0.25P range, k increases with C n increases with the increase of n The larger the value, the greater the bending deflection of the external thread teeth compared to the bending deflection of the internal thread teeth. It can be seen from the equation that when When k is 1, the bending deflection of the internal and external threads is equal. When k < 1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread begins to be smaller than the bending deflection of the internal thread. n When ≤0.125P, the bending deflection of the external thread is not greater than that of the internal thread, and the internal thread can undergo a larger bending deformation to absorb the inertia force generated by the alternating load, thereby further reducing the stress at the bottom of the external thread under the action of the alternating load, thereby further improving the fatigue performance of the external thread.

[0082] In specific applications, the pitch P of the internal thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm.

[0083] In order to verify the superiority of the internal thread provided in this embodiment, a comparative test was conducted. The parameters of the test thread are shown in Table 1. The crest width of thread 1 to thread 3 of the present invention is in the range of 0.025P≤C n ≤0.2P.

[0084] Table 1 Parameters of the thread of the present invention and the comparative thread

[0085]

[0086] According to the above setting parameters, the dynamic analysis of the internal and external threads (the external threads used with the internal threads of the present invention and the comparative internal threads are all standard metric external threads) is performed using general finite element analysis software, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt to obtain the external threads corresponding to threads 1 to 3 and the comparative internal threads at the calibrated position (calibrated position is Figure 5 The average stress variation curve at the red dot in the figure, which is the first thread position of the external thread and is usually the position where the stress is most concentrated, is plotted over time. Figure 6 As shown in the figure, under the action of alternating load, the average stress of the external threads corresponding to threads 1 to 3 at the calibrated position is smaller than the average stress of the external threads corresponding to the internal threads at the calibrated position, and the fatigue performance of the external threads corresponding to threads 1 to 3 is better than that of the external threads corresponding to the internal threads; the crest width C of thread 3 n =0.2P, although the average stress of the external thread corresponding to thread 3 at the calibrated position is less than the average stress of the external thread corresponding to the internal thread at the calibrated position, the average stresses of the two are very close; the crest width C of thread 1 and thread 2 n ≤0.125P, the average stress of the corresponding external thread at the calibrated position is significantly smaller than that of the external thread corresponding to the internal thread.

[0087] Embodiment 2 of the internal thread in the present invention:

[0088] The inventive concept of this embodiment is to reduce the tooth thickness of the internal thread and increase the tooth height of the internal thread, thereby reducing the rigidity of the internal thread and increasing the bending deflection of the internal thread. When the threaded connection pair is subjected to alternating loads, the internal thread can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread.

[0089] Specifically, the internal thread in this embodiment is an improved metric internal thread for use with a standard metric external thread, and the tooth profile of the internal thread in this embodiment is evolved from the tooth profile of the standard metric internal thread, such as Figure 7 As shown, the tooth profile of the internal thread (solid line in the figure) includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The tooth profile angle α of the internal thread is 60°, the pitch is P, and the minor diameter is D1 , tooth height is h n , crest width is C n , the tooth bottom width is C n2 The tooth angle, pitch and minor diameter of the standard metric internal thread are the same as those of the internal thread of this embodiment, and the major diameter of the standard metric internal thread is D and the middle diameter is D 2 , crest width The tooth bottom width is Tooth height is h 0 According to the geometric relationship, we can find

[0090] In this embodiment, the crest width C of the internal thread is n Satisfy 0<C n <C 0 , that is, 0<C n <0.25P, and according to the geometric relationship, we can find Crest width C n He Ya Gao n are variables, among which That is h n The tooth height is greater than that of the standard metric internal thread and less than that at the vertex of the original triangle, ensuring that the tooth profile with a pitch of P and a tooth profile angle α of 60° can still exist. This is equivalent to thinning the tooth thickness of the internal thread teeth in this embodiment, while increasing the tooth height, thereby reducing the rigidity of the internal thread teeth and increasing the bending deflection of the internal thread teeth. When the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread tooth bottom under the action of the alternating load, improving the fatigue performance of the external thread, and solving the problem that the existing external thread has poor fatigue performance, which leads to fatigue fracture of parts such as bolts and studs, and seriously affects the safety and reliability of engineering equipment.

[0091] In order to further explore the optimal range and facilitate subsequent analysis, Figure 8 As shown, in this embodiment, the threads of the internal thread and the standard metric external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0092] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0093]

[0094] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0095] Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0096] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0097] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is where h w is the tooth height of the standard metric external thread, i.e. h w =h 0 , then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0098] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0099]

[0100] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0101]

[0102] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as: This formula can be transformed into:

[0103] According to k and C n and h n The equation plots k as a function of C n and h n Surfaces such as Fig. 9 As shown. When k≤1, That is: 0.464P+0.619C n ≤h n , where 0 <C n <0.25P. That is, Fig. 9 In the curved surface below the k=1 contour line, the bending deflection of the external thread teeth is not greater than that of the internal thread teeth. The bending deflection of the internal thread teeth is larger, and the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, so that the inertia force borne by the external thread teeth is lower, and the fatigue performance of the external thread is better.

[0104] Furthermore, when k≤0.36, That is: 0.542P+0.87C n ≤h n The bending deflection of the external thread teeth is not greater than 0.36 times of the bending deflection of the internal thread teeth, so that the bending deflection of the internal thread teeth is further increased, the inertia force borne by the internal thread teeth is further increased, the inertia force borne by the external thread teeth is further reduced, and the fatigue performance of the external thread is further improved.

[0105] Furthermore, when k≤0.25, 0.578P+0.982C n ≤h n The bending deflection of the external thread teeth is not greater than one-fourth of the bending deflection of the internal thread teeth. The inertial force borne by the internal thread teeth is further increased, the inertial force borne by the external thread teeth is further reduced, and the fatigue performance of the external thread is further improved.

[0106] Furthermore, when k≤0.1, That is: 0.687P+1.333C n ≤h n The bending deflection of the external thread teeth is not greater than one tenth of the bending deflection of the internal thread teeth. The inertial force borne by the internal thread teeth is further increased, the inertial force borne by the external thread teeth is further reduced, and the fatigue performance of the external thread is further improved.

[0107] In specific applications, the pitch P of the internal thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm.

[0108] In order to verify the superiority of the internal thread provided in this embodiment, a comparative test was conducted. The parameters of the test thread are shown in Table 2. The crest width of thread 4 to thread 8 of the present invention is in the range of 0 <C n <0.25P, that is: 0 <C n <1mm. Tooth height range is Right now: Crest width C of thread 4 n With tooth height h n Satisfies the relationship 0.687P+1.333C n =3.015≤h n =3.2; crest width C of thread 5 n With tooth height h n Satisfies the relationship 0.578P+0.982C n =2.703≤h n =3; crest width C of thread 6 n With tooth height h n Satisfies the relationship 0.542P+0.87C n =2.778≤h n =2.8; crest width C of thread 7 n With tooth height h n Satisfies the relationship 0.464P+0.619C n =2.351≤h n =2.4; crest width C of thread 8 n With tooth height h n Satisfies the relationship 0.464P+0.619C n =2.474>h n =2.4.

[0109] Table 2 Parameters of the thread of the present invention and the comparative thread

[0110]

[0111]

[0112] The dynamic analysis of the internal and external threads (the external threads used in conjunction with the internal threads of the present invention and the comparative internal threads are all standard metric external threads) was performed using general finite element analysis software to obtain the average stress variation curve of the external threads corresponding to threads 4 to 8 and the comparative internal threads at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load. Fig.10As shown in the figure, under the action of alternating load, the average stress of the external threads corresponding to threads 4 to 8 at the calibrated position is smaller than the average stress of the external threads corresponding to the comparative internal threads at the calibrated position, and the fatigue properties of the external threads corresponding to threads 4 to 8 are better than those corresponding to the comparative internal threads; although the average stress of the external thread corresponding to thread 8 at the calibrated position is smaller than the average stress of the external thread corresponding to the comparative internal thread at the calibrated position, the average stresses of the two are very close; the deflection ratio of the internal and external threads of threads 4 to 7 is k≤1, and the average stress of the corresponding external threads at the calibrated position is significantly smaller than that of the external threads corresponding to the comparative internal threads.

[0113] Embodiment 3 of the internal thread in the present invention:

[0114] The inventive concept of this embodiment is to reduce the tooth thickness of the internal thread teeth, reduce the rigidity of the internal thread teeth, and increase the bending deflection of the internal thread teeth. Then, when the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread.

[0115] Specifically, the internal thread in this embodiment is an improved MJ internal thread for use with a standard MJ external thread, and the tooth profile of the internal thread in this embodiment is evolved from the tooth profile of the standard MJ internal thread, such as Fig.11 As shown, the tooth profile of the internal thread (solid line in the figure) includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The tooth profile angle α of the internal thread is 60°, the pitch is P, the major diameter is D, and the middle diameter is D 2 , the path is D 1 , tooth height is h n These parameters are the same as those of the standard MJ internal thread, so according to the geometric relationship, we can find

[0116] Different from the standard MJ internal thread, the internal thread of this embodiment has a thinner tooth thickness. The crest width of the internal thread of this embodiment is defined as C n , the tooth bottom width is C n2 , the crest width of the standard MJ internal thread is C 0 According to existing knowledge, Therefore, the crest width C of the internal thread in this embodiment is n Satisfy 0<C n <C 0 , after simplification, we can get 0<C n <0.3125P. In addition, according to the geometric relationship, we can find In this way, while keeping the tooth profile angle at 60°, the crest width C of the internal thread of the present invention is n Compared with the crest width C of the standard MJ internal thread 0 To be small, and the tooth bottom width C n2Compared with the standard MJ internal thread root width To be larger, and the tooth bottom width C n2 With crest width C n A certain geometric relationship is maintained between them, which is equivalent to translating the straight line segment on one side of the tooth profile line. In this way, the rigidity of the internal thread teeth can be reduced by thinning the tooth thickness of the internal thread teeth, and the bending deflection of the internal thread teeth can be increased. Then, when the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress at the bottom of the external thread teeth under the action of the alternating loads, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0117] In order to further explore the crest width C n A better upper limit value is convenient for subsequent analysis, such as Fig.12 As shown, in this embodiment, the threads of the internal thread and the standard MJ external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0118] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0119]

[0120] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0121] Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0122] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0123] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0124] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0125] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0126]

[0127] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as:

[0128]

[0129] In the obtained k about C n In the equation, when 0<C n <0.3125P range, k increases with C n increases with the increase of n The larger the value, the greater the bending deflection of the external thread teeth compared to the bending deflection of the internal thread teeth. It can be seen from the equation that when When k is 1, the bending deflection of the internal and external threads is equal. When k < 1, during the load-bearing process of the internal and external threads, the bending deflection of the external thread begins to be smaller than the bending deflection of the internal thread. n When ≤0.125P, the bending deflection of the external thread is not greater than that of the internal thread, and the internal thread can undergo a larger bending deformation to absorb the inertia force generated by the alternating load, thereby further reducing the stress at the bottom of the external thread under the action of the alternating load, thereby further improving the fatigue performance of the external thread.

[0130] In specific applications, the pitch P of the internal thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm.

[0131] In order to verify the superiority of the internal thread provided in this embodiment, a comparative test was conducted. The parameters of the test thread are shown in Table 3. The crest width of thread 9 to thread 11 of the present invention is in the range of 0.025P≤C n ≤0.2P.

[0132] Table 3 Parameters of the thread of the present invention and the comparative thread

[0133]

[0134] The dynamic analysis of the internal and external threads (the external threads used in conjunction with the internal threads of the present invention and the comparative internal threads are all standard MJ external threads) was performed using general finite element analysis software to obtain the average stress variation curve of the external threads corresponding to threads 9 to 11 and the comparative internal threads at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load. Fig.13 As shown in the figure, under the action of alternating load, the average stress of the external threads corresponding to threads 9 to 11 at the calibrated position is smaller than the average stress of the external threads corresponding to the internal threads at the calibrated position. The fatigue performance of the external threads corresponding to threads 9 to 11 is better than that of the external threads corresponding to the internal threads. The crest width C of thread 11 is n =0.2P, although the average stress of the external thread corresponding to thread 11 at the calibrated position is less than the average stress of the external thread corresponding to the internal thread at the calibrated position, the average stresses of the two are very close; the crest width C of thread 9 and thread 10 n ≤0.125P, the average stress of the corresponding external thread at the calibrated position is significantly smaller than that of the external thread corresponding to the internal thread.

[0135] Embodiment 4 of the internal thread of the present invention:

[0136] The inventive concept of this embodiment is to reduce the tooth thickness of the internal thread and increase the tooth height of the internal thread, thereby reducing the rigidity of the internal thread and increasing the bending deflection of the internal thread. When the threaded connection pair is subjected to alternating loads, the internal thread can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread.

[0137] Specifically, the internal thread in this embodiment is an improved MJ internal thread for use with a standard MJ external thread, and the tooth profile of the internal thread in this embodiment is evolved from the tooth profile of the standard MJ internal thread, such as Fig.14As shown, the tooth profile of the internal thread (solid line in the figure) includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The tooth profile angle α of the internal thread is 60°, the pitch is P, and the minor diameter is D 1 , tooth height is h n , crest width is C n , the tooth bottom width is C n2 The tooth angle, pitch and minor diameter of the standard MJ internal thread are the same as those of the internal thread of this embodiment, and the major diameter of the standard MJ internal thread is D and the middle diameter is D 2 , crest width The tooth bottom width is Tooth height is h 0 According to the geometric relationship, we can find

[0138] The crest width C of the internal thread in this embodiment is n Satisfy 0<C n <C 0 , that is, 0<C n <0.3125P. At the same time, according to the geometric relationship, we can find Crest width C n He Ya Gao n are variables, among which That is h n The tooth height is greater than that of the standard MJ internal thread and less than that at the vertex of the original triangle, ensuring that the tooth profile with a pitch of P and a tooth profile angle α of 60° can still exist. This is equivalent to thinning the tooth thickness of the internal thread teeth in this embodiment, while increasing the tooth height, thereby reducing the rigidity of the internal thread teeth and increasing the bending deflection of the internal thread teeth. When the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread tooth bottom under the action of the alternating load, improving the fatigue performance of the external thread, and solving the problem that the existing external thread has poor fatigue performance, which leads to fatigue fracture of parts such as bolts and studs, and seriously affects the safety and reliability of engineering equipment.

[0139] In order to further explore the optimal range and facilitate subsequent analysis, Fig.15 As shown, in this embodiment, the threads of the internal thread and the standard MJ external thread are simplified into a set of interacting rectangular cantilever beams. The action point Q of the internal and external threads is the midpoint of the overlap area of ​​the internal and external threads. The tooth width of the simplified cantilever beam of the external thread is the tooth width C at the equivalent action point Q. w1 The simplified tooth width of the internal thread is also the tooth width C at the equivalent action point Q. n1 .

[0140] According to the geometric relationship, the tooth width C of the external thread at the equivalent action point P can be calculated. w1 for: Tooth width C of internal thread at equivalent action point P n1 for:

[0141]

[0142] According to the knowledge of material mechanics, the moment of inertia of a rectangular cantilever beam is: Where b is the beam width and h is the beam height.

[0143] Furthermore, the beam height h of the cantilever beam after the internal thread teeth are simplified 内 C n1 , the beam height h of the cantilever beam after the external thread teeth are simplified 外 C w1 , then the simplified cantilever beam moments of inertia of the internal and external threads with beam width b are:

[0144] According to the knowledge of material mechanics, the deflection equation of the cantilever beam at the point of action is: Where F is the load size at the point of action, l is the distance between the point of action and the support position, and E is the elastic modulus of the cantilever beam.

[0145] Assume that the elastic modulus of the material of the external thread is E w The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified external thread teeth at the equivalent action point Q is w for:

[0146]

[0147] Assume that the elastic modulus of the internal thread material is E n The interaction force between the internal and external thread teeth is F, and the length from the equivalent action point Q to the cantilever beam support position is Then the approximate deflection w of the cantilever beam with simplified internal thread teeth at the equivalent action point Q is n for:

[0148]

[0149] Furthermore, the ratio of the external thread deflection to the internal thread deflection is defined as k, then k is:

[0150]

[0151] Generally, the elastic modulus of the internal and external thread materials are approximately equal. For the convenience of analysis, this embodiment takes Therefore, the ratio k of the external thread deflection to the internal thread deflection can be further simplified as: This formula can be transformed into:

[0152]

[0153] According to k and C n and h n The equation plots k as a function of C n and h n Surfaces such as Fig.16 As shown. When k≤1, That is: 0.412P+0.6C n ≤h n , where 0 <C n <0.3125P. That is, Fig.16 In the curved surface below the k=1 contour line, the bending deflection of the external thread teeth is not greater than that of the internal thread teeth. The bending deflection of the internal thread teeth is larger, and the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, so that the inertia force borne by the external thread teeth is lower, and the fatigue performance of the external thread is better.

[0154] Furthermore, when k≤0.55, That is: 0.449P+0.732C n ≤h n The bending deflection of the external thread teeth is not greater than 0.55 times the bending deflection of the internal thread teeth, so that the bending deflection of the internal thread teeth is further increased, the inertia force borne by the internal thread teeth is further increased, the inertia force borne by the external thread teeth is further reduced, and the fatigue performance of the external thread is further improved.

[0155] Furthermore, when k≤0.4, That is: 0.472P+0.814C n ≤h n The bending deflection of the external thread teeth is not greater than 0.4 times the bending deflection of the internal thread teeth, so that the bending deflection of the internal thread teeth is further increased, the inertia force borne by the internal thread teeth is further increased, the inertia force borne by the external thread teeth is further reduced, and the fatigue performance of the external thread is further improved.

[0156] Furthermore, when k≤0.1, that is: 0.607P+1.292C n ≤h n The bending deflection of the external thread teeth is not greater than one tenth of the bending deflection of the internal thread teeth. The inertial force borne by the internal thread teeth is further increased, the inertial force borne by the external thread teeth is further reduced, and the fatigue performance of the external thread is further improved.

[0157] In specific applications, the pitch P of the internal thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm.

[0158] In order to verify the superiority of the internal thread provided in this embodiment, a comparative test was conducted. The parameters of the test thread are shown in Table 4. The crest width of the thread 12 to the thread 16 of the present invention is in the range of 0 <C n <0.3125P, that is: 0 <C n <1.25mm. Tooth height range is Right now: Crest width C of thread 12 n With tooth height h n Satisfies the relationship 0.607P+1.292C n =2.944≤h n =3; crest width C of thread 13 n With tooth height h n Satisfies the relationship 0.472P+0.814C n =2.378≤h n =2.8; crest width C of thread 14 n With tooth height h n Satisfies the relationship 0.449P+0.732C n =2.383≤h n =2.6; crest width C of thread 15 n With tooth height h n Satisfies the relationship 0.412P+0.6C n =2.248≤h n =2.4; crest width C of thread 16 n With tooth height h n Satisfies the relationship 0.412P+0.6C n =2.368>h n =2;

[0159] Table 4 Parameters of the thread of the present invention and the comparative thread

[0160]

[0161]

[0162] The dynamic analysis of the internal and external threads (the external threads used in conjunction with the internal threads of the present invention and the comparative internal threads are all standard MJ external threads) was performed using general finite element analysis software to obtain the average stress variation curve of the external threads corresponding to threads 12 to 16 and the comparative internal threads at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load. Fig.17 As shown in the figure, under the action of alternating load, the average stress of the external threads corresponding to threads 12 to 16 at the calibrated position is smaller than the average stress of the external threads corresponding to the comparative internal threads at the calibrated position, and the fatigue properties of the external threads corresponding to threads 12 to 16 are better than those corresponding to the comparative internal threads; although the average stress of the external thread corresponding to thread 16 at the calibrated position is smaller than the average stress of the external thread corresponding to the comparative internal thread at the calibrated position, the average stresses of the two are very close; the internal and external thread tooth deflection ratio k≤1 of threads 12 to 15, the average stress of the corresponding external threads at the calibrated position is significantly smaller than that of the external threads corresponding to the comparative internal threads.

[0163] The embodiment of the threaded connection pair in the present invention is as follows: the threaded connection pair includes an internal thread and an external thread used in conjunction with the internal thread, the external thread is a standard metric thread or MJ thread, and the structure of the internal thread is the same as the internal thread of the above embodiment, which will not be repeated here.

[0164] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the protection scope of the present invention.

Claims

1. An internal thread, which is a metric thread or an MJ thread and the thread profile of the internal thread includes a crest, a straight line segment, a root and a straight line segment connected in sequence, the thread angle of the internal thread is 60°, the pitch is P, and the crest width is defined as C n , the tooth bottom width is C n2 , tooth height is h n , characterized in that: 0<C n <C0, Where C0 is the crest width of the standard metric internal thread or MJ internal thread.

2. The internal thread according to claim 1, characterized in that: Where h0 is the thread height of the standard metric internal thread or MJ internal thread.

3. The internal thread according to claim 2, characterized in that: The internal thread is a metric internal thread used in conjunction with a standard metric external thread. According to the fact that the bending deflection of a rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than the bending deflection of a rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that 4. The internal thread according to claim 3, characterized in that: According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than 0.36 times the bending deflection of the rectangular cantilever beam after the thread teeth are simplified.

5. The internal thread according to claim 4, characterized in that: According to the bending deflection of the simplified rectangular cantilever beam of the standard metric external thread is not greater than one-fourth of the bending deflection of the simplified rectangular cantilever beam of the internal thread, it can be concluded that 6. The internal thread according to claim 5, characterized in that: According to the fact that the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the standard metric external thread is not greater than one tenth of the bending deflection of the rectangular cantilever beam simplified by the thread teeth of the internal thread, it can be concluded that 7. The internal thread according to claim 2, characterized in that: The internal thread is an MJ internal thread used in conjunction with a standard MJ external thread. According to the fact that the bending deflection of a rectangular cantilever beam simplified by the thread teeth of the standard MJ external thread is not greater than the bending deflection of a rectangular cantilever beam simplified by the thread teeth of the internal thread, it is concluded that 8. The internal thread according to claim 7, characterized in that: According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than 0.55 times the bending deflection of the rectangular cantilever beam after the thread teeth are simplified.

9. The internal thread according to claim 8, characterized in that: According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than 0.4 times the bending deflection of the rectangular cantilever beam after the thread teeth are simplified.

10. The internal thread according to claim 9, characterized in that: According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than one tenth of the bending deflection of the rectangular cantilever beam after the thread teeth are simplified.

11. The internal thread according to claim 1, characterized in that: The internal thread is a metric internal thread used in conjunction with a standard metric external thread. According to the standard metric external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, it is concluded that 0<C n ≤0.125P.

12. The internal thread according to claim 1, characterized in that: The internal thread is an MJ internal thread used in conjunction with the standard MJ external thread. According to the standard MJ external thread, the bending deflection of the rectangular cantilever beam after the thread teeth are simplified is not greater than the bending deflection of the rectangular cantilever beam after the thread teeth are simplified, so 0<C n ≤0.125P.

13. A threaded connection pair, comprising an internal thread and an external thread used in conjunction with the internal thread, wherein the external thread is a standard metric thread or MJ thread, characterized in that: The internal thread is the internal thread according to any one of claims 1 to 12.

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