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 threads are meter threads or MJ threads, the thread angle of the internal threads is 60 degrees, the thread pitch is P, and continuous grooves are formed in the tooth bottoms of the internal threads. A thread molded line of the internal thread comprises a thread top, a thread side linear section, a groove side linear section corresponding to one groove side wall of the groove, a groove bottom section corresponding to the groove bottom wall of the groove, a groove side linear section corresponding to the other groove side wall of the groove and a thread side linear section which are connected in sequence; the tooth thickness of the internal thread teeth is reduced, the tooth height of the internal thread teeth can be further increased, the rigidity of the internal thread teeth is reduced, the bending deflection of the internal thread teeth is improved, the internal thread teeth can generate larger bending deformation to absorb inertia force generated by alternating loads, and the internal thread teeth can be further prevented from being damaged. The stress of the root of the external thread under the action of 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 both internal and external threads includes the crest, straight line segment, root 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, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 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 type 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 crest, straight line segment, root 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, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 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 MJ internal threads 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 bending deformation, and the adjacent external thread teeth will have a tendency to open due to the action of the internal thread. This tendency will produce a large 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, has a tooth angle of 60°, a pitch of P, a continuous groove at the root of the internal thread, a tooth line of the internal thread including a tooth top, a tooth side straight line segment, a groove side straight line segment corresponding to one groove side wall of the groove, a groove bottom segment corresponding to the groove bottom wall of the groove, a groove side straight line segment corresponding to the other groove side wall of the groove, and a tooth side straight line segment connected in sequence, and the maximum width of the groove is g,

[0009] The beneficial effect of the above technical solution is that: the present invention belongs to an improved invention creation, the improvement is that a continuous groove is arranged at the root of the internal thread, the tooth profile of the internal thread includes a tooth top, a tooth side straight line segment, a groove side straight line segment corresponding to one of the groove side walls of the groove, a groove bottom segment corresponding to the groove bottom wall of the groove, a groove side straight line segment corresponding to the other groove side wall of the groove, and a tooth side straight line segment connected in sequence, the maximum width of the groove is g, and the present invention limits g to be greater than It is the tooth bottom width of the standard metric internal thread or MJ internal thread, which means that the groove side wall of the groove has been processed to the tooth side, which is equivalent to reducing the tooth thickness of the internal thread tooth. In this way, the rigidity of the internal thread tooth can be reduced and the bending deflection of the internal thread tooth can be increased. At this time, the internal thread tooth is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread tooth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, 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, which seriously affects the safety and reliability of engineering equipment. At the same time, the present invention also limits g to less than Avoid the groove being too wide to affect the basic tooth thickness of the internal thread teeth, ensuring safety in use.

[0010] Furthermore, the maximum depth of the groove is h, where h n It is the tooth height of standard metric internal thread or MJ internal thread.

[0011] Furthermore, the internal thread is a metric thread.

[0012] Furthermore, the internal thread is an MJ thread.

[0013] Furthermore, the maximum depth of the groove is h,

[0014] To achieve the above purpose, the threaded connection pair in the present invention adopts the following technical solution:

[0015] A threaded connection pair, comprising an internal thread and a standard external thread used in conjunction with the internal thread, wherein the internal thread and the standard external thread are both metric threads or MJ threads, the internal thread has a tooth profile angle of 60°, a pitch of P, a continuous groove is arranged at the root of the internal thread, the tooth profile of the internal thread comprises a tooth top, a tooth side straight line segment, a groove side straight line segment corresponding to one groove side wall of the groove, a groove bottom segment corresponding to the groove bottom wall of the groove, a groove side straight line segment corresponding to the other groove side wall of the groove, and a tooth side straight line segment connected in sequence, the maximum width of the groove is g,

[0016] The beneficial effect of the above technical solution is that: the present invention belongs to an improved invention creation, the improvement is that a continuous groove is arranged at the root of the internal thread, the tooth profile of the internal thread includes a tooth top, a tooth side straight line segment, a groove side straight line segment corresponding to one of the groove side walls of the groove, a groove bottom segment corresponding to the groove bottom wall of the groove, a groove side straight line segment corresponding to the other groove side wall of the groove, and a tooth side straight line segment connected in sequence, the maximum width of the groove is g, and the present invention limits g to be greater than It is the tooth bottom width of the standard metric internal thread or MJ internal thread, which means that the groove side wall of the groove has been processed to the tooth side, which is equivalent to reducing the tooth thickness of the internal thread. In this way, the rigidity of the internal thread can be reduced and the bending deflection of the internal thread can be increased. The external thread is a standard metric thread or MJ thread, and the external thread does not change. At this time, the internal thread is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread can bend and deform more to absorb the inertia force generated by the alternating load, thereby reducing the stress of the external thread 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, which seriously affects the safety and reliability of engineering equipment. At the same time, the present invention also limits g to less than Avoid the groove being too wide to affect the basic tooth thickness of the internal thread teeth, ensuring safety in use.

[0017] Furthermore, the maximum depth of the groove is h, where h n It is the tooth height of standard metric internal thread or MJ internal thread.

[0018] Furthermore, the internal thread is a metric thread.

[0019] Furthermore, the internal thread is an MJ thread.

[0020] Furthermore, the maximum depth of the groove is h, BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a tooth profile diagram of a standard metric thread in the prior art;

[0022] Figure 2 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0023] Figure 3 The figure is a tooth profile diagram of the internal thread embodiment 1 of the present invention;

[0024] Figure 4 This is a tooth profile diagram of internal thread embodiment 2 of the present invention;

[0025] Figure 5 It is a schematic diagram of the calibration position of the internal thread of the present invention;

[0026] Figure 6 It is a curve diagram of the average stress at the calibrated position changing with time under the action of alternating load in the internal thread embodiment 1 and embodiment 2 of the present invention;

[0027] Figure 7 The figure is a tooth profile diagram of the internal thread embodiment 3 of the present invention;

[0028] Figure 8 The figure is a tooth profile diagram of the internal thread embodiment 4 of the present invention;

[0029] Fig. 9 It is a curve diagram of the average stress at the calibrated position changing with time under the action of alternating load in the internal thread embodiment 3 and embodiment 4 of the present invention;

[0030] Fig.10 This is the tooth profile diagram of internal thread embodiment 5 of the present invention. DETAILED DESCRIPTION

[0031] In view of the technical problems existing in the prior art, the basic concept of the present invention is to process a groove on the tooth bottom of a standard metric internal thread or an MJ internal thread, and limit the maximum width of the groove to be greater than the tooth bottom width of the standard metric internal thread or the MJ internal thread, so that the groove side wall of the groove is processed to the tooth side, thereby reducing the tooth thickness of the internal thread tooth, reducing the rigidity of the internal thread tooth, and increasing the bending deflection of the internal thread tooth. When the threaded connection pair is subjected to alternating loads, the internal thread tooth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby improving the fatigue performance of the external thread.

[0032] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0033] Embodiment 1 of the internal thread of the present invention:

[0034] The internal thread in this embodiment is a metric internal thread used in conjunction with a standard metric external thread, and the internal thread is improved from the standard metric internal thread, such as Figure 3 As shown in the figure, the tooth angle α of the improved internal thread is 60°, the pitch is P, the major diameter is D, the middle diameter is D2, the minor diameter is D1, and the tooth height is The crest width is These parameters are the same as standard metric internal threads.

[0035] Different from the prior art, the improved internal thread has a continuous groove at its bottom, so that the tooth profile of the internal thread includes a tooth top 11, a tooth side straight line segment 12, a groove side straight line segment 13 corresponding to one of the groove side walls of the groove, a groove bottom segment 14 corresponding to the groove bottom wall of the groove, a groove side straight line segment 13 corresponding to the other groove side wall of the groove, and a tooth side straight line segment 12, which are connected in sequence. The groove bottom segment 14 is arc-shaped, and the two tooth side straight line segments 12 are symmetrical and equal in length. The angle between the two tooth side straight line segments 12 is the tooth profile angle α. In this embodiment, the two groove side straight line segments 13 are equal in length and are both perpendicular to the axis of the internal thread. The spacing between the two groove side straight line segments 13 is the groove width of the groove (also the maximum width of the groove). The groove width is defined as g and the maximum depth of the groove is defined as h. Then

[0036] because According to the geometric relationship, the inner diameter at the deepest part of the groove is the major diameter D of the standard metric internal thread, that is, the tooth height of the internal thread in this embodiment is equal to the tooth height of the standard metric internal thread, which is At the same time, the present invention limits the slot width g to be greater than It is the standard metric internal thread root width, which means that the groove sidewalls have been processed to the tooth side, which is equivalent to reducing the tooth thickness of the internal thread teeth. In this way, the rigidity of the internal thread teeth can be reduced and the bending deflection of the internal thread teeth can be increased. At this time, the internal thread teeth are equivalent to a spring with reduced rigidity. 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 root under the action of the alternating loads and improving the fatigue performance of the external thread. At the same time, the present invention also limits the groove width g to less than Avoid the groove being too wide to affect the basic tooth thickness of the internal thread teeth, ensuring safety in use.

[0037] Embodiment 2 of the internal thread in the present invention:

[0038] The internal thread in this embodiment is a metric internal thread used in conjunction with a standard metric external thread, and the internal thread is improved from the standard metric internal thread, such as Figure 4 As shown in the figure, the improved internal thread has a tooth angle α of 60°, a pitch of P, a minor diameter of D1, and a tooth crest width of The standard metric internal thread height is The major diameter is D, the middle diameter is D2, and the tooth bottom width is

[0039] The improved internal thread has a continuous groove at its bottom, so that the internal thread tooth profile includes a tooth top 11, a tooth side straight line segment 12, a groove side straight line segment 13 corresponding to one of the groove side walls of the groove, a groove bottom segment 14 corresponding to the groove bottom wall of the groove, a groove side straight line segment 13 corresponding to the other groove side wall of the groove, and a tooth side straight line segment 12, which are connected in sequence. The groove bottom segment 14 is arc-shaped, and the two tooth side straight line segments 12 are symmetrical and equal in length. The angle between the two tooth side straight line segments 12 is the tooth profile angle α. In this embodiment, the two groove side straight line segments 13 are equal in length and are both perpendicular to the axis of the internal thread. The spacing between the two groove side straight line segments 13 is the groove width of the groove (i.e., the maximum width of the groove). The groove width is defined as g and the maximum depth of the groove is defined as h. Then

[0040]

[0041] From the geometric relationship, we know that when When the inner diameter of the deepest groove is just the major diameter D of the standard metric internal thread, the embodiment defines This indicates that the maximum depth of the groove has exceeded the major diameter D of the standard metric internal thread, so the actual tooth height of the internal thread will be greater than the tooth height of the standard metric internal thread, which increases the tooth height of the internal thread, reduces the rigidity of the internal thread teeth, and increases the bending deflection of the internal thread teeth. The tooth height of the entire internal thread cannot be increased to more than twice the original value to ensure the safe use of the internal thread.

[0042] In addition, the present invention defines the groove width g as greater than It is the standard metric internal thread root width, which means that the groove sidewalls have been processed to the tooth side, so that on the basis of increasing the tooth height, the internal thread tooth thickness is reduced at the same time, thereby further reducing the rigidity of the internal thread tooth and increasing the bending deflection of the internal thread tooth. At this time, the internal thread tooth is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread tooth can undergo greater bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress of the external thread root under the action of the alternating load and improving the fatigue performance of the external thread. At the same time, the present invention also limits the groove width g to less than Avoid the groove being too wide to affect the basic tooth thickness of the internal thread teeth, ensuring safety in use.

[0043] The following provides a comparative test for Example 1 and Example 2, and the specific parameters are shown in Table 1, where the pitch of threads 1 to 3 is P = 4mm, the major diameter of the internal threads of threads 1 and 3 is D = 36mm, the major diameter of the standard internal thread corresponding to thread 2 is D = 36mm, threads 1 to 3 are improved metric internal threads, and the comparative thread is a standard metric internal thread with a pitch of P = 4mm and a major diameter of D = 36mm. By calculation, it can be obtained

[0044] Table 1 Parameters of thread in this application and comparison thread

[0045]

[0046] It can be seen from Table 1 that the groove width g1 of thread 1 and the groove width g2 of thread 2 are equal, both are 1mm, and both are within In the range, it can be calculated Maximum depth of thread 1 groove Therefore, thread 1 is equivalent to only reducing the tooth thickness of the internal thread teeth.

[0047] Maximum depth of thread 2 groove certainly Therefore, thread 2 reduces the tooth thickness of the internal thread teeth and increases the tooth height of the internal thread teeth.

[0048] The groove width of thread 3 is g3 = 1.5 mm. In the range, it can be calculated Maximum depth of thread 3 grooves Therefore, thread 3 also only reduces the tooth thickness of the internal thread teeth, but thread 3 is reduced more than thread 1.

[0049] According to the above setting parameters, the internal and external threads (the external threads used with the internal threads of the present invention and the comparative threads are all standard metric external threads) are subjected to dynamic analysis using general finite element analysis software, that is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is imposed on the bolt, and the external threads corresponding to threads 1 to 3 and the comparative threads are obtained at the calibrated position (calibrated position is Figure 5 The red dot in the figure is the first buckle position of the external thread and the internal thread, which is usually the position where the stress is most concentrated. The average stress changes with time curve at the red dot position, which is the first buckle position of the external thread and the internal thread, and is usually the position where the stress is most concentrated.

[0050] The average stress variation curve is as follows: Figure 6 As shown in Table 2, 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 comparison threads at the calibrated position. Table 2 shows the stress amplitude (the difference between the maximum stress and the minimum stress on the stress curve) of the external threads corresponding to threads 1 to 3 and the comparison threads at the calibrated position. The smaller the amplitude, the smaller the load amplitude when the thread is subjected to the alternating load. Therefore, combined with Figure 6 It can be seen from Table 2 that the stress amplitude of the external threads corresponding to threads 1 to 3 is smaller than that of the comparison threads, and the fatigue performance of the external threads corresponding to threads 1 to 3 is better than that of the comparison threads. At the same time, the stress amplitude of the external thread corresponding to thread 2 is the smallest, which proves that the fatigue performance of the external thread will be better improved under the dual measures of increasing the tooth height and reducing the tooth thickness. Similarly, in the case of only reducing the tooth thickness, the stress amplitude of the external thread corresponding to thread 3 is smaller than that of the external thread corresponding to thread 1, indicating that the larger the groove width, the more the tooth thickness is reduced, the more the stiffness of the internal thread teeth decreases, and the corresponding fatigue performance of the external thread will be better.

[0051] Table 2 Stress amplitude of external threads corresponding to the threads of the present application and the comparative threads

[0052] Thread 1 Thread 2 Thread 3 Contrast thread 115.47MPa 113.422MPa 113.53MPa 116.697MPa

[0053] Embodiment 3 of the internal thread in the present invention:

[0054] The internal thread in this embodiment is an MJ internal thread used in conjunction with a standard MJ external thread, and the internal thread is improved from the standard MJ internal thread. Figure 7 As shown in the figure, the tooth angle α of the improved internal thread is 60°, the pitch is P, the major diameter is D, the middle diameter is D2, the minor diameter is D1, and the tooth height is The crest width is These parameters are the same as those of standard MJ internal threads.

[0055] Different from the prior art, the improved internal thread has a continuous groove at its bottom, so that the tooth profile of the internal thread includes a tooth top 11, a tooth side straight line segment 12, a groove side straight line segment 13 corresponding to one of the groove side walls of the groove, a groove bottom segment 14 corresponding to the groove bottom wall of the groove, a groove side straight line segment 13 corresponding to the other groove side wall of the groove, and a tooth side straight line segment 12, which are connected in sequence. The groove bottom segment 14 is arc-shaped, and the two tooth side straight line segments 12 are symmetrical and equal in length. The angle between the two tooth side straight line segments 12 is the tooth profile angle α. In this embodiment, the two groove side straight line segments 13 are equal in length and are both perpendicular to the axis of the internal thread. The spacing between the two groove side straight line segments 13 is the groove width of the groove (i.e., the maximum width of the groove). The groove width is defined as g and the maximum depth of the groove is defined as h. Then

[0056] because According to the geometric relationship, the inner diameter at the deepest part of the groove is the major diameter D of the standard MJ internal thread, that is, the tooth height of the internal thread in this embodiment is equal to the tooth height of the standard MJ internal thread, which is At the same time, the present invention limits the slot width g to be greater than It is the standard MJ internal thread root width, which means that the groove sidewalls have been processed to the tooth side, which is equivalent to reducing the tooth thickness of the internal thread teeth. In this way, the rigidity of the internal thread teeth can be reduced and the bending deflection of the internal thread teeth can be increased. At this time, the internal thread teeth are equivalent to a spring with reduced rigidity. 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 root under the action of the alternating loads and improving the fatigue performance of the external thread. At the same time, the present invention also limits the groove width g to less than Avoid the groove being too wide to affect the basic tooth thickness of the internal thread teeth, ensuring safety in use.

[0057] Embodiment 4 of the internal thread of the present invention:

[0058] The internal thread in this embodiment is an MJ internal thread used in conjunction with a standard MJ external thread, and the internal thread is improved from the standard MJ internal thread. Figure 8 As shown in the figure, the improved internal thread has a tooth angle α of 60°, a pitch of P, a minor diameter of D1, and a tooth crest width of The standard MJ internal thread height is The major diameter is D, the middle diameter is D2, and the tooth bottom width is

[0059] The improved internal thread has a continuous groove at its bottom, so that the internal thread tooth profile includes a tooth top 11, a tooth side straight line segment 12, a groove side straight line segment 13 corresponding to one of the groove side walls of the groove, a groove bottom segment 14 corresponding to the groove bottom wall of the groove, a groove side straight line segment 13 corresponding to the other groove side wall of the groove, and a tooth side straight line segment 12, which are connected in sequence. The groove bottom segment 14 is arc-shaped, and the two tooth side straight line segments 12 are symmetrical and equal in length. The angle between the two tooth side straight line segments 12 is the tooth profile angle α. In this embodiment, the two groove side straight line segments 13 are equal in length and are both perpendicular to the axis of the internal thread. The spacing between the two groove side straight line segments 13 is the groove width of the groove (i.e., the maximum width of the groove). The groove width is defined as g and the maximum depth of the groove is defined as h. Then

[0060]

[0061] From the geometric relationship, we know that when The inner diameter of the deepest groove is just the major diameter D of the standard MJ internal thread, and in this embodiment, it is defined as This indicates that the maximum depth of the groove has exceeded the major diameter D of the standard MJ internal thread, so the actual tooth height of the internal thread will be greater than the tooth height of the standard MJ internal thread, which increases the tooth height of the internal thread, reduces the rigidity of the internal thread teeth, and increases the bending deflection of the internal thread teeth. The tooth height of the entire internal thread cannot be increased to more than twice the original value to ensure the safe use of the internal thread.

[0062] In addition, the present invention defines the groove width g as greater than It is the standard MJ internal thread root width, which means that the groove sidewalls have been processed to the tooth side, so that on the basis of increasing the tooth height, the tooth thickness of the internal thread teeth is reduced at the same time, thereby further reducing the rigidity of the internal thread teeth and increasing the bending deflection of the internal thread teeth. At this time, the internal thread teeth are equivalent to a spring with reduced rigidity. 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 root under the action of the alternating loads and improving the fatigue performance of the external thread. At the same time, the present invention also limits the groove width g to less than Avoid the groove being too wide to affect the basic tooth thickness of the internal thread teeth, ensuring safety in use.

[0063] The following provides a comparative test for Example 3 and Example 4, and the specific parameters are shown in Table 3, where the pitch of threads 4 to 6 is P = 4mm, the major diameter of the internal threads of threads 4 and 6 is D = 36mm, the major diameter of the standard internal thread corresponding to thread 5 is D = 36mm, threads 4 to 6 are improved MJ internal threads, and the comparative thread is a standard MJ internal thread with a pitch of P = 4mm and a major diameter of D = 36mm. By calculation, it can be obtained

[0065] Table 3 Parameters of thread in this application and comparison thread

[0066]

[0067] It can be seen from Table 3 that the groove width g4 of thread 4 and the groove width g5 of thread 5 are equal, both are 1mm, and both are within In the range, it can be calculated Maximum depth of thread 4 grooves Therefore, thread 4 is equivalent to only reducing the tooth thickness of the internal thread teeth.

[0068] Maximum depth of thread 5 grooves at the same time Therefore, thread 5 reduces the tooth thickness of the internal thread teeth and increases the tooth height of the internal thread teeth.

[0069] The groove width of thread 6 is g6 = 1.5 mm. In the range, it can be calculated Maximum depth of thread 6 grooves Therefore, thread 6 also only reduces the tooth thickness of the internal thread teeth, but thread 6 is reduced more than thread 4.

[0070] According to the above setting parameters, the internal and external threads (the external threads used in conjunction with the internal threads of the present invention and the comparison threads are all standard MJ external threads) are subjected to dynamic analysis using general finite element analysis software, that is, a fixed constraint is imposed on the nut, and an alternating load that varies with time is imposed on the bolt, and the average stress variation curve of the external threads corresponding to threads 4 to 6 and the comparison threads at the calibrated position (the calibrated position is the same as above) under the same alternating load is obtained.

[0071] The average stress variation curve is as follows: Fig. 9 As shown in the figure, the average stress of the external threads corresponding to threads 4 to 6 at the calibrated position is less than the average stress of the external threads corresponding to the comparison threads at the calibrated position, so the fatigue performance of the external threads corresponding to threads 4 to 6 is better than that of the comparison threads. At the same time, the average stress of the external threads corresponding to thread 5 at the calibrated position is the smallest, which proves that the fatigue performance of the external threads will be better improved under the dual measures of increasing tooth height and reducing tooth thickness. Similarly, in the case of only reducing tooth thickness, the average stress of the external threads corresponding to thread 6 at the calibrated position is less than that of thread 4, which means that the larger the groove width, the more the tooth thickness is reduced, the more the stiffness of the internal thread teeth decreases, and the corresponding fatigue performance of the external threads will be better.

[0072] Embodiment 5 of the internal thread of the present invention: Fig.10As shown, this embodiment is different from any of the above embodiments in that the two groove side straight sections 13 of the internal thread bottom groove are not perpendicular to the internal thread axis, and the two groove side straight sections 13 are still symmetrical but have a certain angle between them, which is smaller than the tooth angle. At this time, the maximum depth of the groove is h, the maximum width is g, and the maximum width position is the position where the groove side straight section 13 intersects with the tooth side straight section 12.

[0073] In other embodiments of the internal thread: Different from any of the above embodiments, the bottom section of the groove is a straight line section, and the groove depth at each location of the groove is the same.

[0074] The embodiment of the threaded connection pair in the present invention is as follows: the threaded connection pair includes an internal thread and a standard external thread used in conjunction with the internal thread. The internal thread is the internal thread in any of the above embodiments and will not be repeated here.

[0075] 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, has a thread angle of 60° and a pitch of P, and is characterized in that: The root of the internal thread is provided with a continuous groove. The tooth profile of the internal thread includes a tooth top, a tooth side straight line segment, a groove side straight line segment corresponding to one of the groove side walls of the groove, a groove bottom segment corresponding to the groove bottom wall of the groove, a groove side straight line segment corresponding to the other groove side wall of the groove, and a tooth side straight line segment connected in sequence. The maximum width of the groove is g.

2. The internal thread according to claim 1, characterized in that: The maximum depth of the groove is h, where h n It is the tooth height of standard metric internal thread or MJ internal thread.

3. The internal thread according to claim 2, characterized in that: The internal thread is metric thread.

4. The internal thread according to claim 2, characterized in that: The internal thread is MJ thread.

5. The internal thread according to claim 1, characterized in that: The maximum depth of the groove is h, 6. A threaded connection pair, comprising an internal thread and a standard external thread used in conjunction with the internal thread, wherein the internal thread and the standard external thread are both metric threads or MJ threads, the internal thread has a thread angle of 60° and a pitch of P, and is characterized in that: The root of the internal thread is provided with a continuous groove. The tooth profile of the internal thread includes a tooth top, a tooth side straight line segment, a groove side straight line segment corresponding to one of the groove side walls of the groove, a groove bottom segment corresponding to the groove bottom wall of the groove, a groove side straight line segment corresponding to the other groove side wall of the groove, and a tooth side straight line segment connected in sequence. The maximum width of the groove is g.

7. The threaded connection pair according to claim 6, characterized in that: The maximum depth of the groove is h, where h n It is the tooth height of standard metric internal thread or MJ internal thread.

8. The threaded connection pair according to claim 7, characterized in that: The internal thread is metric thread.

9. The threaded connection pair according to claim 7, characterized in that: The internal thread is MJ thread.

10. The threaded connection pair according to claim 6, characterized in that: The maximum depth of the groove is h,

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