Threaded connection pair and internal thread

Abstract

The invention provides a threaded connection pair and an internal thread, and belongs to the technical field of threaded connection. The internal thread is a meter-made internal thread or an MJ internal thread used for being matched with a standard meter-made external thread or an MJ external thread for use, and a thread molded line of the internal thread comprises a thread top, a thread side straight line section, a thread bottom and a thread side straight line section which are sequentially connected. The included angle beta between at least one tooth side straight line section, located at the axial end, in the tooth-shaped line of the internal thread and the plane perpendicular to the axis of the internal thread is larger than 10 degrees and smaller than 30 degrees. The equivalent action point between the internal thread tooth and the external thread tooth is close to the position of the root of the external thread tooth, the torque borne by the external thread tooth is greatly reduced, the opening effect of the internal thread tooth on the external thread tooth is effectively weakened, the stress concentration of the root of the external thread tooth is relieved, and meanwhile the rigidity of the external thread tooth is larger than that of the internal thread tooth; the internal thread teeth serve as energy absorption boxes of the external thread teeth, the average stress of the root of the external thread teeth is effectively reduced, and the fatigue performance of the external thread is improved.

Description

Technical Field

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

[0002] Thread fatigue fracture is a particularly critical technical problem in the engineering field, especially in equipment and components that are subjected to high stress and long service time, its impact cannot be ignored. Among various threaded connection structures, metric thread and MJ thread are the most widely used threaded connection forms. The tooth profile shape of standard metric internal thread and MJ internal thread is the same, such as Figure 1 As shown, the tooth profile of the internal thread includes the tooth top 11, the tooth side straight line segment 12, the tooth bottom 13, and the tooth side straight line segment 2 14 connected in sequence. In the figure, D is the major diameter of the internal thread, D2 is the middle diameter of the internal thread, D1 is the minor diameter of the internal thread, P is the pitch, and h is the pitch. n C is the internal thread height, n is the tooth crest width, α w is the tooth profile angle, that is, the angle between the tooth side straight line segment 12 and the tooth side straight line segment 2 14, tooth profile angle α w is 60°.

[0003] External threads are compatible with internal threads, and the external thread profile angle is also 60°. The thread height is equal to the internal thread height. Therefore, when the internal and external threads are subjected to load, the straight line segments of the internal and external thread flanks contact simultaneously, making the equivalent action point of the internal and external threads closer to the external thread crest. If the external thread is regarded as a cantilever beam, the distance between the equivalent action point and the external thread root is the equivalent force arm. The equivalent force arm has a certain length, causing the external thread to be subjected to a larger torque, which in turn causes the internal thread to exert a greater opening effect on the external thread, resulting in significant stress concentration at the external thread root.

[0004] At the same time, since the equivalent action points of the internal and external threads are closer to the top of the external thread, and the tooth width at the top of the external thread is smaller, the tooth width of the internal thread at the equivalent action point is larger, resulting in the stiffness of the external thread being smaller than that of the internal thread. When the internal and external threads are subjected to alternating loads, the inertia force between the internal and external threads is in an unbalanced state. The external thread with smaller thread stiffness acts as an energy absorption box for the internal thread with larger stiffness, absorbing the inertia force between the internal and external threads, which increases the average stress at the bottom of the external thread, resulting in poor fatigue performance of the external thread. Summary of the Invention

[0005] The purpose of the present invention is to provide an internal thread to solve the problem that the existing internal thread causes poor fatigue performance of the external thread; the purpose of the present invention is also to provide a threaded connection pair to solve the above problem.

[0006] To achieve the above purpose, the internal thread in the present invention adopts the following technical solutions:

[0007] An internal thread is a metric internal thread or an MJ internal thread for use with a standard metric external thread or an MJ external thread. The internal thread profile includes a tooth top, a tooth side straight line segment, a tooth bottom and a tooth side straight line segment connected in sequence. The angle between the tooth side straight line segment at least at the axial end of the internal thread profile and a plane perpendicular to the axis of the internal thread is β, and 10°<β<30°.

[0008] The beneficial effect of the above technical solution is that the present invention is an improved invention and further defines the tooth profile of the internal thread. The angle between the tooth side straight segment at least at the axial end of the tooth profile of the internal thread and the plane perpendicular to the axis of the internal thread is β, 10°<β<30°, while it is well known that the tooth profile angle of the standard metric external thread or MJ external thread is 60°, and the angle between the tooth side straight segment of the standard metric external thread or MJ external thread and the plane perpendicular to the axis of the external thread is 30 degrees, that is, the tooth profile half angle is 30 degrees. In addition, it is well known that when a threaded connection pair is subjected to load, stress concentration usually occurs at the first three thread positions, that is, the axial end of the internal thread. Therefore, when the internal thread of the present invention is used in conjunction with the standard metric external thread or MJ external thread, the tooth side straight segments of the internal and external thread teeth can no longer fit together, and the contact point is located at the tooth bottom position of the external thread, that is, the tooth top position of the internal thread. Because the contact point is far from the root of the internal thread, when the internal thread is under load, the top of the internal thread will undergo a certain degree of bending deformation, resulting in partial contact between the internal and external threads. The equivalent force arm between the equivalent action point between the internal and external threads and the root of the external thread is shorter, which greatly reduces the torque borne by the external thread. This can greatly weaken the opening effect of the internal thread on the external thread, reduce the stress concentration at the root of the external thread, reduce the stress at the root of the external thread, and improve the fatigue performance of the external thread. At the same time, the closer the equivalent action point is to the root of the external thread, the larger the tooth width of the external thread at the equivalent action point, and the greater the stiffness of the external thread. The tooth width of the internal thread at the equivalent action point becomes smaller, and the stiffness of the internal thread decreases. When subjected to alternating loads, the internal thread can act as an energy absorption box for the external thread, effectively reducing the average stress at the root of the external thread and improving the fatigue performance of the external thread.

[0009] Furthermore, 24°≤β≤29°.

[0010] Furthermore, the angles between each straight line segment of the tooth profile of the internal thread toward one axial end and the plane perpendicular to the axis of the internal thread are 30°, and the angles between each straight line segment of the tooth profile of the internal thread toward the other axial end and the plane perpendicular to the axis of the internal thread are β.

[0011] Furthermore, the internal thread is a metric internal thread, and the thread height is hn , The crest width of the internal thread is C n ,

[0012] Furthermore, the internal thread is an MJ thread, and the tooth height of the internal thread is h n , The crest width of the internal thread is C n ,

[0013] To achieve the above objectives, the threaded connection pair in the present invention adopts the following technical solutions:

[0014] A threaded connection pair includes an internal thread and an external thread used in conjunction with the internal thread, the external thread being a standard metric external thread or MJ external thread, and the internal thread being an improved metric internal thread or MJ internal thread, the tooth profile of the internal thread including a tooth top, a tooth side straight line segment, a tooth bottom, and a tooth side straight line segment connected in sequence, the angle β between the tooth side straight line segment at least at the axial end of the tooth profile of the internal thread and a plane perpendicular to the axis of the internal thread being 10°<β<30°.

[0015] The beneficial effect of the above technical solution is that the present invention is an improved invention and further defines the tooth profile of the internal thread. The angle between the tooth side straight segment at least at the axial end of the tooth profile of the internal thread and the plane perpendicular to the axis of the internal thread is β, 10°<β<30°, while it is well known that the tooth profile angle of the standard metric external thread or MJ external thread is 60°, and the angle between the tooth side straight segment of the standard metric external thread or MJ external thread and the plane perpendicular to the axis of the external thread is 30 degrees, that is, the tooth profile half angle is 30 degrees. In addition, it is well known that when a threaded connection pair is subjected to load, stress concentration usually occurs at the first three thread positions, that is, the axial end of the internal thread. Therefore, when the internal thread of the present invention is used in conjunction with the standard metric external thread or MJ external thread, the tooth side straight segments of the internal and external thread teeth can no longer fit together, and the contact point is located at the tooth bottom position of the external thread, that is, the tooth top position of the internal thread. Because the contact point is far from the root of the internal thread, when the internal thread is under load, the top of the internal thread will undergo a certain degree of bending deformation, resulting in partial contact between the internal and external threads. The equivalent force arm between the equivalent action point between the internal and external threads and the root of the external thread is shorter, which greatly reduces the torque borne by the external thread. This can greatly weaken the opening effect of the internal thread on the external thread, reduce the stress concentration at the root of the external thread, reduce the stress at the root of the external thread, and improve the fatigue performance of the external thread. At the same time, the closer the equivalent action point is to the root of the external thread, the larger the tooth width of the external thread at the equivalent action point, and the greater the stiffness of the external thread. The tooth width of the internal thread at the equivalent action point becomes smaller, and the stiffness of the internal thread decreases. When subjected to alternating loads, the internal thread can act as an energy absorption box for the external thread, effectively reducing the average stress at the root of the external thread and improving the fatigue performance of the external thread.

[0016] Furthermore, 24°≤β≤29°.

[0017] Furthermore, the angles between each straight line segment of the tooth profile of the internal thread toward one axial end and the plane perpendicular to the axis of the internal thread are 30°, and the angles between each straight line segment of the tooth profile of the internal thread toward the other axial end and the plane perpendicular to the axis of the internal thread are β.

[0018] Furthermore, the internal thread is a metric internal thread, and the thread height is h n , The crest width of the internal thread is C n ,

[0019] Furthermore, the internal thread is an MJ thread, and the tooth height of the internal thread is h n , The crest width of the internal thread is C n , BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the tooth profile diagram of metric internal thread and MJ internal thread in the prior art;

[0021] Figure 2 1. The tooth profile diagram of the internal thread in the embodiment 1 of the threaded connection pair of the present invention;

[0022] Figure 3 Schematic diagram of embodiment 1 of the threaded connection pair of the present invention;

[0023] Figure 4 Schematic diagram of the force acting on the external thread in Example 1 of the threaded connection pair of the present invention;

[0024] Figure 5 Schematic diagram of the calibration position of the external thread in Example 1 of the threaded connection pair of the present invention;

[0025] Figure 6 This is a graph showing the change in average stress over time at a calibrated position of an external thread (36 mm major diameter, 4 mm pitch) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention under alternating loads;

[0026] Figure 7 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s under alternating load for an external thread (major diameter 36mm, pitch 4mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention;

[0027] Figure 8 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s under alternating load for an external thread (major diameter 36mm, pitch 4mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention as a function of β;

[0028] Figure 9 The thread load ratio of each turn of the external thread used in conjunction with the internal threads of four different β values in Example 1 of the threaded connection pair of the present invention;

[0029] Figure 10 This is a graph showing the change in average stress over time at a calibrated position of an external thread (with a major diameter of 42 mm and a pitch of 4.5 mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention under alternating loads;

[0030] Figure 11 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s under alternating load for an external thread (major diameter 42mm, pitch 4.5mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention as a function of β;

[0031] Figure 12 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s under alternating load for an external thread (major diameter 42mm, pitch 4.5mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention as a function of β;

[0032] Figure 13 This is a graph showing the change in average stress over time at a calibrated position of an external thread (with a major diameter of 48 mm and a pitch of 5 mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention under alternating loads;

[0033] Figure 14 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s under alternating load for an external thread (major diameter 48mm, pitch 5mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention;

[0034] Figure 15 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s under alternating load for an external thread (major diameter 48mm, pitch 5mm) used in conjunction with eight internal threads with different β values in Example 1 of the threaded connection pair of the present invention as a function of β;

[0035] Figure 16 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s with β for three groups of external threads with different major diameters and pitches under alternating loads in Example 1 of the threaded connection pair of the present invention;

[0036] Figure 17 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s with β for three groups of external threads with different major diameters and pitches under alternating loads in Example 1 of the threaded connection pair of the present invention;

[0037] Figure 18 This is a graph showing the change in average stress over time at a calibrated position of an external thread (36 mm major diameter, 4 mm pitch) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention under alternating loads;

[0038] Figure 19 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s under alternating load for an external thread (major diameter 36mm, pitch 4mm) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention;

[0039] Figure 20This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s under alternating load for an external thread (major diameter 36mm, pitch 4mm) used in conjunction with internal threads of eight different β values in Example 2 of the threaded connection pair of the present invention as a function of β;

[0040] Figure 21 The thread load ratio of each turn of the external thread used in conjunction with the internal thread of four different β values in Example 2 of the threaded connection pair of the present invention;

[0041] Figure 22 This is a graph showing the change in average stress over time at a calibrated position of an external thread (with a major diameter of 42 mm and a pitch of 4.5 mm) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention under alternating loads;

[0042] Figure 23 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s under alternating load for an external thread (major diameter 42mm, pitch 4.5mm) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention as a function of β;

[0043] Figure 24 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s under alternating load for an external thread (major diameter 42mm, pitch 4.5mm) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention as a function of β;

[0044] Figure 25 This is a graph showing the change in average stress over time at a calibrated position of an external thread (with a major diameter of 48 mm and a pitch of 5 mm) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention under alternating loads;

[0045] Figure 26 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s under alternating load for an external thread (major diameter 48mm, pitch 5mm) used in conjunction with eight internal threads with different β values in Example 2 of the threaded connection pair of the present invention;

[0046] Figure 27 This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0075s with β for an external thread (major diameter of 48mm, pitch of 5mm) used in conjunction with eight internal threads with different β values under alternating load in Example 2 of the threaded connection pair of the present invention;

[0047] Figure 28This is a graph showing the variation of the average stress at the calibrated position at the loading time of 0.0025s with β for three groups of external threads with different major diameters and pitches under alternating loads in Example 2 of the internal thread of the present invention;

[0048] Figure 29 This is a graph showing the change in average stress versus β at the calibrated position at the loading time of 0.0075s for three groups of external threads with different major diameters and pitches under alternating load in Example 2 of the internal thread of the present invention.

[0049] In the figure: 11, tooth top; 12, tooth side straight line segment 1; 13, tooth bottom; 14, tooth side straight line segment 2; 2, internal thread; 21, tooth top; 22, tooth side straight line segment 1; 23, tooth bottom; 24, tooth side straight line segment 2; 3, external thread. DETAILED DESCRIPTION

[0050] In response to the technical problems existing in the prior art, the basic concept of the present invention is to change the tooth profile angle of the internal thread so that the angle between the straight line segment of the tooth profile of the internal thread and the plane perpendicular to the axis of the internal thread is greater than 10° and less than 30°, thereby making it impossible for the straight line segments of the tooth profile of the internal and external threads to touch each other, and the contact point is located at the bottom of the tooth of the external thread, which greatly reduces the torque borne by the external thread teeth, increases the stiffness of the external thread teeth, and improves the fatigue performance of the external thread.

[0051] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0052] Embodiment 1 of the threaded connection pair of the present invention:

[0053] like Figure 2 and Figure 3 As shown, the threaded connection pair is based on a bolt and a nut, and includes an internal thread 2 provided on the nut and an external thread 3 provided on the bolt and used in conjunction with the internal thread 2. The external thread 3 is a standard metric external thread, so the tooth angle of the external thread 3 is 60°.

[0054] Internal thread 2 is an improved metric internal thread, such as Figure 2As shown, the tooth profile of the internal thread 2 includes a crest 21, a flank straight segment 1 22, a root 23, and a flank straight segment 2 24, which are connected in sequence. Each flank straight segment in the tooth profile of the internal thread 2, which faces one axial end, is a flank straight segment 1 22. The angle between each flank straight segment 1 22 and a plane perpendicular to the internal thread axis is 30°. The angle between flank straight segment 24 and a plane perpendicular to the internal thread axis is β. Furthermore, each flank straight segment in the tooth profile of the internal thread, which faces the other axial end, is a flank straight segment 24. The angle between each flank straight segment 24 and a plane perpendicular to the internal thread axis is β, with 10° < β < 30°. The angle between flank straight segment 1 22 and flank straight segment 24 is the tooth profile angle α of the internal thread 2, with α < 60°.

[0055] In addition, the major diameter of the internal thread is D, the medium diameter is D2, the minor diameter is D1, the pitch is P, and the crest width of the internal thread is C n , The tooth height of the internal thread is h n According to the geometric relationship, Therefore, the crest width C of the internal thread in this embodiment is n The same as the standard metric internal thread crest width, tooth height h n The tooth height is the same as that of the standard metric internal thread, and only the angle of each tooth side straight line segment 24 facing the same axial end is changed.

[0056] like Figure 3 and Figure 4 As shown in the figure, because β is less than 30°, when the internal thread is used with a standard metric external thread, the straight lines on the flanks of the internal and external threads no longer fit together. The contact point is located at the root of the external thread, which is also the crest of the internal thread. Because the contact point is far from the root of the internal thread, when the internal thread is under load, the crest of the internal thread will undergo a certain degree of bending deformation, resulting in partial contact between the internal and external threads, with the equivalent action point at position F1. However, the straight lines on the flanks of the standard metric internal thread and the external thread fit together, resulting in a larger contact area and an equivalent action point closer to the crest of the external thread, which is position F2.

[0057] The equivalent force arm between the equivalent action point between the internal and external threads and the bottom of the external thread is shorter, which greatly reduces the torque on the external thread. This can significantly weaken the opening effect of the internal thread on the external thread, reduce stress concentration at the bottom of the external thread, reduce stress at the bottom of the external thread, and improve the fatigue performance of the external thread. At the same time, the closer the equivalent action point is to the bottom of the external thread, the larger the tooth width of the external thread at the equivalent action point, and the greater the stiffness of the external thread. The smaller the tooth width at the equivalent action point of the internal thread, the lower the stiffness of the internal thread. When subjected to alternating loads, the internal thread acts as an energy absorber for the external thread, effectively reducing the average stress at the bottom of the external thread and improving the fatigue performance of the external thread.

[0058] In addition, since 10°<β, it avoids the local stress concentration of the external thread teeth caused by too small β, which in turn reduces fatigue performance. Furthermore, 24°≤β≤29°, within this range, the fatigue performance of the external thread can be further improved. The specific verification process is as follows:

[0059] This embodiment provides 8 kinds of internal threads with different β values (30°, 29.5°, 29°, 27°, 24°, 22°, 20°, 12°) for comparison. The major diameter of all internal threads is 36mm and the pitch is 4mm. The external threads used in conjunction with each internal thread are all standard metric threads, with a major diameter of 36mm and a pitch of 4mm. The general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt. Under the same alternating load, the external threads corresponding to the 8 kinds of internal threads are at the calibrated position (the calibrated position is Figure 5 The average stress variation curve at the red dot position 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 the time curve ( Figure 6 Table 1 shows the stress amplitudes of the external threads corresponding to the eight types of internal threads at the calibrated positions. The stress amplitude is the difference between the maximum stress and the minimum stress on the stress curve. The smaller the amplitude, the smaller the load amplitude the thread will bear when subjected to alternating loads, and the better the fatigue performance.

[0060] Table 1 Stress amplitudes at the calibration position of the external thread (major diameter 36 mm, pitch 4 mm) corresponding to 8 types of metric internal threads

[0061] tooth half angle β＝30° β＝29.5° β＝29° β＝27° Stress amplitude 134.170Mpa 130.769Mpa 128.779Mpa 118.850Mpa tooth half angle β＝24° β＝22° β＝20° β＝12° Stress amplitude 107.228Mpa 103.542Mpa 102.116Mpa 99.322Mpa

[0062] As can be seen from Table 1, when β = 29.5°, 29°, 27°, 24°, 22°, 20°, and 12°, the stress amplitude is smaller than when β = 30° (standard metric thread), and the stress amplitude is negatively correlated with β, that is, the smaller β is, the greater the stress amplitude reduction is. Figure 6 It can be seen that the smaller β is, the smaller the average stress is. On the contrary, when β=27°, the average stress is the smallest.

[0063] Figure 7 The figure shows the curve of the average stress of the external thread at the calibrated position under the action of alternating load as a function of β at the loading time of 0.0025s, which is the moment of maximum stress. Figure 8The figure shows the curve of the average stress at the calibration position of the external thread under alternating load at the loading time of 0.0075s, which is the moment of minimum stress. At both loading times, the average stress changes with the decrease of β, showing a trend of first decreasing and then increasing. The initial decrease is because the equivalent action point between the internal and external thread teeth is close to the tooth bottom position of the external thread, which improves the fatigue performance of the external thread. However, as β decreases, it is difficult for the internal thread teeth to achieve greater contact with the external thread teeth through bending deformation. The contact phenomenon between the tips of the internal and external threads becomes more and more obvious, and a relatively large contact stress is generated between the internal and external threads. Under the influence of contact stress, the high stress area of contact and the high stress caused by the opening trend coincide, resulting in an increasing trend of the average stress at the calibration position. This is why the average stress first decreases and then increases, and there is a valley value.

[0064] in addition, Figure 9 The figure shows the load ratios for each turn of the external thread for internal thread angles of β = 30°, 29°, 27°, and 20°. As can be seen from the figure, the smaller the internal thread angle, the more uniform the load distribution across the corresponding external thread turns. This improved load uniformity helps improve the fatigue performance of external threads. In contrast, in existing standard metric threaded connections, the first three turns of thread near the support surface (for example, the end face of the nut used to press against the connected parts, in the case of a bolt and nut), bear 70% of the total load, with the first turn bearing the greatest load. Because the stiffness of the internal thread is significantly lower than that of the external thread when the internal and external threads are in contact, the internal thread of the present invention is more susceptible to elastic deformation as the axial force of the bolt increases, compared to existing thread structures. This is particularly true for the first turn of the thread. When the bolt is subjected to the same axial load, assuming the same bending deformation, the first turn of the internal thread of the present invention has less stiffness and generates less axial force. Consequently, the threads after the first turn bear more axial load, thus improving thread load uniformity and, in turn, enhancing the fatigue performance of the threaded connection.

[0065] For comparison, this embodiment also provides comparative test results of internal threads with 8 different β values (30°, 29.5°, 29°, 27°, 25°, 22°, 20°, and 12°) when the major diameter of the internal and external threads is 42 mm and the pitch is 4.5 mm. The average stress variation curve of the external threads corresponding to the 8 internal threads at the calibrated position over time is shown as follows: Figure 10 As shown in Table 2, the stress amplitudes of the external threads corresponding to the eight types of internal threads at the calibrated positions are shown. Figure 11 and Figure 12 This is the curve of the average stress of the external thread at the calibration position at the loading time of 0.0025s and 0.0075s under alternating load as a function of β.

[0066] Table 2 Stress amplitudes at the calibration position of the external threads (large diameter 42 mm, pitch 4.5 mm) corresponding to 8 types of metric internal threads

[0067]

[0068]

[0069] In addition, this embodiment also provides comparative test results of internal threads with 8 different β values (30°, 29.5°, 29°, 27°, 25°, 22°, 20°, and 12°) when the major diameter of the internal and external threads is 48 mm and the pitch is 5 mm. The average stress variation curves of the external threads corresponding to the 8 internal threads at the calibrated position over time are shown as follows: Figure 13 As shown in Table 3, the stress amplitudes of the external threads corresponding to the eight types of internal threads at the calibrated positions are shown. Figure 14 and Figure 15 This is the curve of the average stress of the external thread at the calibration position at the loading time of 0.0025s and 0.0075s under alternating load as a function of β.

[0070] Table 3 Stress amplitudes at the calibration position of the external threads (large diameter 48 mm, pitch 5 mm) corresponding to 8 types of metric internal threads

[0071] tooth half angle β＝30° β＝29.5° β＝29° β＝27° Stress amplitude 149.442Mpa 146.331Mpa 144.361Mpa 134.643Mpa tooth half angle β＝25° β＝22° β＝20° β＝12° Stress amplitude 126.303Mpa 117.245Mpa 115.37Mpa 110.633Mpa

[0072] The test results above show that when the external thread has a major diameter of 42 mm and a pitch of 4.5 mm, and a major diameter of 48 mm and a pitch of 5 mm, the stress amplitude gradually decreases with decreasing β, but the average stress is not at its minimum when β is minimum. Furthermore, the average stress trends at loading times of 0.0025 s and 0.0075 s are the same: they first decrease and then increase with decreasing β.

[0073] Combining the above three sets of data, we can get Figure 16 and Figure 17 The curves of the average stress variation with β at the calibration position at the loading moments of 0.0025s and 0.0075s for the three groups of external threads with different major diameters and pitches under alternating loads are shown. Considering that there is a valley value in the average stress, and the valley value changes with the difference in the major diameter and pitch of the thread, and also changes with the difference in the load, it is difficult to accurately determine the β value corresponding to the valley value. Therefore, the present invention takes a preferred range, i.e., 24°≤β≤29°. The average stress within this range is relatively low, and the valley value is included. At the same time, the average stress corresponding to the two β end values is almost the same.

[0074] Embodiment 2 of the threaded connection pair of the present invention:

[0075] Unlike Example 1, the internal thread in this embodiment is an improved MJ thread, and the external thread used with the internal thread is a standard MJ external thread. The shape of the internal thread profile is the same as in Example 1, that is, the internal thread profile also includes a crest, a flank straight segment, a root, and a flank straight segment connected in sequence. The angle between each flank straight segment in the internal thread profile facing one axial end and a plane perpendicular to the internal thread axis is 30°, and the angle between each flank straight segment in the internal thread profile facing the other axial end and a plane perpendicular to the internal thread axis is β, where 10°<β<30°. The angle between adjacent flank straight segments is the internal thread profile angle α, where α<60°.

[0076] Since the internal thread in this embodiment is an MJ thread, the crest width of the internal thread is C n , The tooth height of the internal thread is h n According to the geometric relationship, Therefore, the crest width C of the internal thread in this embodiment is n The same as the standard MJ internal thread crest width, tooth height h n The tooth height is the same as that of the standard MJ internal thread, and only the angle of the straight line segment of each tooth side facing the same axial end is changed.

[0077] Similarly, because β is less than 30°, when an internal thread is used with a standard MJ external thread, the straight lines on the flanks of the internal and external threads no longer fit together. The contact point is located at the root of the external thread, or the crest of the internal thread. Because the contact point is far from the root of the internal thread, when the internal thread is under load, the crest of the internal thread will bend and deform to a certain extent, resulting in partial contact between the internal and external threads. However, the straight lines on the flanks of a standard MJ internal thread fit closely to the external thread, resulting in a larger contact area and an equivalent contact point closer to the crest of the external thread.

[0078] The equivalent force arm between the equivalent action point between the internal and external threads and the root of the external thread is shorter, which greatly reduces the torque on the external thread and significantly weakens the opening effect of the internal thread on the external thread, alleviating stress concentration at the root of the external thread, reducing stress at the root of the external thread, and improving the fatigue performance of the external thread. At the same time, the closer the equivalent action point is to the root of the external thread, the larger the tooth width of the external thread at the equivalent action point, and the greater the stiffness of the external thread. The smaller the tooth width of the internal thread at the equivalent action point, the lower the stiffness of the internal thread. When subjected to alternating loads, the internal thread acts as an energy absorber for the external thread, effectively reducing the average stress at the root of the external thread and improving the fatigue performance of the external thread.

[0079] In addition, since 10°<β, it avoids the local stress concentration of the external thread teeth caused by too small β, which in turn reduces fatigue performance. Furthermore, 24°≤β≤29°, within this range, the fatigue performance of the external thread can be further improved. The specific verification process is as follows:

[0080] This embodiment provides 8 kinds of internal threads with different β values (30°, 29.5°, 29°, 27°, 24°, 22°, 20°, 12°) for comparison. The major diameter of all internal threads is 36mm, and the pitch is 4mm. The external threads used in conjunction with each internal thread are all standard MJ threads, and the major diameter of the external thread is 36mm and the pitch is 4mm. The general finite element analysis software is used to perform dynamic analysis on the internal and external threads, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt. Under the same alternating load, the average stress variation curve of the external threads corresponding to the 8 kinds of internal threads at the calibration position (the calibration position is the same as in Example 1) is obtained. Figure 18 Table 4 shows the stress amplitudes of the external threads corresponding to the eight types of internal threads at the calibrated positions.

[0081] Table 4 Stress amplitudes at the calibration position of the external threads (major diameter 36 mm, pitch 4 mm) corresponding to 8 types of MJ internal threads

[0082] tooth half angle β＝30° β＝29.5° β＝29° β＝27° Stress amplitude 133.162Mpa 130.375Mpa 128.758Mpa 119.008Mpa tooth half angle β＝24° β＝22° β＝20° β＝12° Stress amplitude 109.022Mpa 102.362Mpa 100.592Mpa 98.066Mpa

[0083] It can be seen from Table 4 that when β = 29.5°, 29°, 27°, 24°, 22°, 20°, and 12°, the stress amplitude is smaller than that when β = 30° (standard MJ thread), and the stress amplitude is negatively correlated with β, that is, the smaller β is, the greater the stress amplitude reduction is. Figure 18 It can be seen that the smaller β is, the smaller the average stress is. On the contrary, when β=27°, the average stress is the smallest.

[0084] Figure 19 The figure shows the curve of the average stress of the external thread at the calibrated position under the action of alternating load as a function of β at the loading time of 0.0025s, which is the moment of maximum stress. Figure 20The figure shows the curve of the average stress at the calibration position of the external thread under alternating load at the loading time of 0.0075s, which is the moment of minimum stress. At both loading times, the average stress changes with the decrease of β, showing a trend of first decreasing and then increasing. The initial decrease is because the equivalent action point between the internal and external thread teeth is close to the tooth bottom position of the external thread, which improves the fatigue performance of the external thread. However, as β decreases, it is difficult for the internal thread teeth to achieve greater contact with the external thread teeth through bending deformation. The contact phenomenon between the tips of the internal and external threads becomes more and more obvious, and a relatively large contact stress is generated between the internal and external threads. Under the influence of contact stress, the high stress area of contact and the high stress caused by the opening trend coincide, resulting in an increasing trend of the average stress at the calibration position. This is why the average stress first decreases and then increases, and there is a valley value.

[0085] in addition, Figure 21 The figure shows the load ratios for each turn of the external thread for internal thread angles of β = 30°, 29°, 27°, and 20°. As can be seen from the figure, the smaller the internal thread angle, the more uniform the load distribution across the corresponding external thread turns. This improved load uniformity helps improve the fatigue performance of external threads. In contrast, in existing standard MJ threaded connections, the first three turns of thread near the support surface (in the case of the bolt and nut, the support surface is the end face of the nut that compresses the connected parts) bear 70% of the total load, with the first turn bearing the greatest load. Because the stiffness of the internal thread is significantly lower than that of the external thread when the internal and external threads are in contact, the internal thread of the present invention is more susceptible to elastic deformation as the axial force of the bolt increases, compared to existing thread structures. This is particularly true for the first turn of the thread. When the bolt is subjected to the same axial load, assuming the bending deformation of the threads is the same, the first turn of the internal thread of the present invention has less stiffness and generates less axial force. Consequently, the threads after the first turn bear more axial load, thus improving thread load uniformity and, in turn, enhancing the fatigue performance of the threaded connection.

[0086] For comparison, this embodiment also provides comparative test results of internal threads with 8 different β values (30°, 29.5°, 29°, 27°, 25°, 22°, 20°, and 12°) when the major diameter of the internal and external threads is 42 mm and the pitch is 4.5 mm. The average stress variation curve of the external threads corresponding to the 8 internal threads at the calibrated position over time is shown as follows: Figure 22 As shown in Table 5, the stress amplitudes of the external threads corresponding to the eight types of internal threads at the calibrated positions are shown. Figure 23 and Figure 24 This is the curve of the average stress of the external thread at the calibration position at the loading time of 0.0025s and 0.0075s under alternating load as a function of β.

[0087] Table 5 Stress amplitudes at the calibration position of the external threads (large diameter 42 mm, pitch 4.5 mm) corresponding to 8 types of MJ internal threads

[0088] tooth half angle β＝30° β＝29.5° β＝29° β＝27° Stress amplitude 140.582Mpa 137.7Mpa 135.953Mpa 128.051Mpa tooth half angle β＝25° β＝22° β＝20° β＝12° Stress amplitude 119.952Mpa 112.474Mpa 109.289Mpa 104.344Mpa

[0089] In addition, this embodiment also provides comparative test results of internal threads with 8 different β values (30°, 29.5°, 29°, 27°, 25°, 22°, 20°, and 12°) when the major diameter of the internal and external threads is 48 mm and the pitch is 5 mm. The average stress variation curves of the external threads corresponding to the 8 internal threads at the calibrated position over time are shown as follows: Figure 25 As shown in Table 6, the stress amplitudes of the external threads corresponding to the eight types of internal threads at the calibrated positions are shown. Figure 26 and Figure 27 This is the curve of the average stress of the external thread at the calibration position at the loading time of 0.0025s and 0.0075s under alternating load as a function of β.

[0090] Table 6 Stress amplitudes at the calibration position of the external threads (large diameter 48 mm, pitch 5 mm) corresponding to 8 types of MJ internal threads

[0091] tooth half angle β＝30° β＝29.5° β＝29° β＝27° Stress amplitude 149.746Mpa 146.9Mpa 145.337Mpa 137.354Mpa tooth half angle β＝25° β＝22° β＝20° β＝12° Stress amplitude 126.381Mpa 118.195Mpa 114.84Mpa 109.969Mpa

[0092] The test results above show that when the external thread has a major diameter of 42 mm and a pitch of 4.5 mm, and a major diameter of 48 mm and a pitch of 5 mm, the stress amplitude gradually decreases with decreasing β, but the average stress is not at its minimum when β is minimum. Furthermore, the average stress trends at loading times of 0.0025 s and 0.0075 s are the same: they first decrease and then increase with decreasing β.

[0093] Combining the above three sets of data, we can get Figure 28 and Figure 29 The curves of the average stress variation with β at the calibration position at the loading moments of 0.0025s and 0.0075s for the three groups of external threads with different major diameters and pitches under alternating loads are shown. Considering that there is a valley value in the average stress, and the valley value changes with the difference in the major diameter and pitch of the thread, and also changes with the difference in the load, it is difficult to accurately determine the β value corresponding to the valley value. Therefore, the present invention takes a preferred range, i.e., 24°≤β≤29°. The average stress within this range is relatively low, and the valley value is included. At the same time, the average stress corresponding to the two β end values is almost the same.

[0094] In other embodiments of the threaded connection pair: the tooth height h of the internal thread n It can be not the standard internal thread height, but greater than the standard internal thread height. For example, when the internal thread is metric thread, the tooth height is When the internal thread is MJ thread, the tooth height In these cases, the stiffness of the internal thread will be further reduced, which can further reduce the average stress at the root of the external thread and help to further improve the fatigue performance of the external thread.

[0095] In other embodiments of the threaded connection pair, the optimal range of β may also be 24°≤β≤29.5° or 25°≤β≤29° or 25°≤β≤29.5° or 23°≤β≤29.5° or 23°≤β≤29°, all of which include the valley value of the mean stress.

[0096] In other embodiments of the threaded connection pair: the optimal range of β can also be 28.5°≤β≤29.5° or 28.5°≤β≤29°. At this time, the average stress corresponding to the β range is in an ascending range, but the maximum value is smaller than β=30°, so the fatigue performance of the external thread can also be improved.

[0097] In other embodiments of the threaded connection pair: the lower limit value of β can also be 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21° or 22°, and the upper limit value of β can be 27°, 26°, 25°, 24° or 23°. Although at certain loading moments, the average stress value corresponding to β is higher than the average stress value when β = 30°, the stress amplitude corresponding to β does not exceed the stress amplitude when β = 30°, and the average stress value corresponding to β is small at most moments, so overall the fatigue performance of the external thread can still be improved.

[0098] In other embodiments of the threaded connection pair: only the tooth side straight segments of the first three threads of the internal thread and the external thread can be set to an angle β with the plane perpendicular to the axis of the internal thread, or the tooth side straight segments of the first two threads can be set to an angle β with the plane perpendicular to the axis of the internal thread, or only the tooth side straight segments of the end thread can be set to an angle β with the plane perpendicular to the axis of the internal thread, that is, there is no need to set the tooth side straight segments of the internal thread thread line facing the same axial end to an angle β with the plane perpendicular to the axis of the internal thread, because the first three threads are where stress is more concentrated, so these settings can improve the fatigue performance of the external thread at the force concentrated position. Of course, the range of β can be the range given in any of the above embodiments.

[0099] The embodiment of the internal thread in the present invention is as follows: the specific structure of the internal thread is the same as the internal thread in any of the above-mentioned threaded connection embodiments, and will not be repeated here.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the description and drawings of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An internal thread, which is a metric internal thread or an MJ internal thread for use with a standard metric external thread or an MJ external thread, wherein the thread profile of the internal thread comprises a tooth top, a tooth side straight segment, a tooth bottom and a tooth side straight segment connected in sequence, characterized in that: The included angle between at least the tooth side straight line segment at the axial end of the tooth profile of the internal thread and the plane perpendicular to the axis of the internal thread is β, and 10°<β<30°.

2. The internal thread according to claim 1, characterized in that 24°≤β≤29°。 3. The internal thread according to claim 1 or 2, characterized in that: The angles between the straight line segments of the tooth profile of the internal thread toward one axial end and the plane perpendicular to the axis of the internal thread are all 30°, and the angles between the straight line segments of the tooth profile of the internal thread toward the other axial end and the plane perpendicular to the axis of the internal thread are all β.

4. The internal thread according to claim 1 or 2, characterized in that The internal thread is a metric internal thread, and the internal thread height is h n , The crest width of the internal thread is C n , 5. The internal thread according to claim 1 or 2, characterized in that: The internal thread is MJ thread, and the internal thread height is h n , The crest width of the internal thread is C n , 6. 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 external thread or an MJ external thread, and the internal thread is an improved metric internal thread or an MJ internal thread, wherein the tooth profile of the internal thread comprises a tooth top, a tooth side straight segment, a tooth bottom, and a tooth side straight segment connected in sequence, and wherein: The included angle between at least the tooth side straight line segment at the axial end of the tooth profile of the internal thread and the plane perpendicular to the axis of the internal thread is β, and 10°<β<30°.

7. The threaded connection pair according to claim 6, characterized in that: 24°≤β≤29°。 8. The threaded connection pair according to claim 6 or 7, characterized in that: The angles between the straight line segments of the tooth profile of the internal thread toward one axial end and the plane perpendicular to the axis of the internal thread are all 30°, and the angles between the straight line segments of the tooth profile of the internal thread toward the other axial end and the plane perpendicular to the axis of the internal thread are all β.

9. The threaded connection pair according to claim 6 or 7, characterized in that: The internal thread is a metric internal thread, and the internal thread height is h n , The crest width of the internal thread is C n , 10. The threaded connection pair according to claim 6 or 7, characterized in that: The internal thread is MJ thread, and the internal thread height is h n , The crest width of the internal thread is C n ,

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