A kind of arc thread connection pair, inner arc thread and nut

Abstract

The application provides a circular-arc threaded connection pair, an inner circular-arc thread and a nut, and belongs to the technical field of threaded connection. The circular-arc threaded connection pair comprises an inner circular-arc thread and an outer circular-arc thread matched with each other. The tooth profile of the inner circular-arc thread comprises an inner tooth bottom circular-arc, an inner tooth side straight line segment, an inner tooth top straight line segment and an inner tooth side straight line segment connected in sequence. The tooth profile of the outer circular-arc thread comprises an outer thread top, an outer tooth side straight line segment, an outer tooth bottom circular-arc and an outer tooth side straight line segment connected in sequence. The width of the inner tooth top straight line segment is defined as C n , the tooth height of the inner circular-arc thread is defined as h n , the slenderness ratio of the inner circular-arc thread tooth is defined as γ, and the value range of γ is 0.341-0.352. In the application, the inner circular-arc thread tooth is more slender and has smaller rigidity, and is more likely to be bent and deformed. When the inner and outer circular-arc threads bear alternating loads, the inner circular-arc thread tooth can absorb inertial force through bending deformation, thereby reducing the bending deformation of the outer circular-arc thread tooth and improving the fatigue performance of the outer circular-arc thread.

Description

Technical Field

[0001] This invention relates to an arc threaded connection pair, an internal arc thread, and a nut, belonging to the field of threaded connection technology. Background Technology

[0002] Thread fatigue fracture is a critical technical challenge in engineering, particularly in equipment and components subjected to high stress and long-term service, where its impact is significant. Existing threads are generally designed based on static load safety, typically featuring a larger internal thread thickness, such as metric and MJ threads. The average tooth thickness of these internal threads is greater than that of their corresponding external threads, resulting in higher stiffness. During load-bearing, the internal thread exhibits less bending deformation, stronger load-bearing capacity, and is less prone to stripping. However, excessive internal thread stiffness reduces the fatigue performance of the external thread. This is because when subjected to axial alternating loads, the threads vibrate with the alternating load. The internal thread, due to its higher stiffness, experiences less bending deformation, while the external thread requires greater deformation to absorb the inertial force generated by the alternating load. This increases the bending moment on the external thread, leading to a significant increase in high stress at the thread root, thus increasing the risk of fatigue fracture.

[0003] Chinese utility model patent CN209818480U discloses a high-strength circular arc threaded connection pair, which includes a bolt and a nut. The bolt has an external circular arc thread, and the nut has an internal circular arc thread. The tooth profile of the external circular arc thread includes, in sequence, an external thread root arc, an external thread flank straight segment, an external thread crest arc, and an external thread flank straight segment, the latter being tangent to both the external thread root arc and the external thread crest arc. The tooth profile of the internal circular arc thread includes, in sequence, an internal thread root arc, an internal thread flank straight segment, an internal thread crest straight segment, and an internal thread flank straight segment, the latter being tangent to the internal thread root arc.

[0004] When the above-mentioned circular arc threaded connection pair is in use, the straight section of the external thread side and the straight section of the internal thread side are in close contact. By designing a large circular arc structure at the root of the external circular arc thread, the high stress concentration generated at the root of the external circular arc thread is reduced. At the same time, the average tooth thickness of the internal circular arc thread is smaller than that of the external circular arc thread. These designs improve the fatigue performance of the external circular arc thread to a certain extent, but the improvement effect is limited. The fatigue performance of the external circular arc thread is still relatively poor, and fatigue fracture is prone to occur in actual use. Summary of the Invention

[0005] The purpose of this invention is to provide a circular arc threaded connection pair to solve the problem of poor fatigue performance of the outer circular arc thread in existing circular arc threaded connection pairs; the purpose of this invention is also to provide an inner circular arc thread, which can improve the fatigue performance of the outer circular arc thread when used in conjunction with existing outer circular arc threads; the purpose of this invention is also to provide a nut, which can improve the fatigue performance of the outer circular arc thread on existing bolts or studs when used in conjunction with existing bolts or studs.

[0006] To achieve the above objectives, the circular arc threaded connection pair in this invention adopts the following technical solution:

[0007] A circular arc threaded connection pair includes mating internal and external circular arc threads. The tooth profile of the internal circular arc thread includes, in sequence, an internal root arc, an internal flank straight segment, an internal crest straight segment, and an internal flank straight segment. The tooth profile of the external circular arc thread includes, in sequence, an external crest, an external flank straight segment, an external root arc, and an external flank straight segment. The width of the internal crest straight segment is defined as C. n The tooth height of the internal circular arc thread is h. n The slenderness ratio of the inner circular arc thread teeth is... The value of γ ranges from 0.21 to 0.508.

[0008] The beneficial effects of the above technical solution are as follows: This invention is an improved invention, further limiting the width C of the straight segment of the internal tooth crest. n tooth height h of the internal circular arc thread n The ratio of the two values ​​constitutes the slenderness ratio γ of the internal circular arc thread, and the value of γ ranges from 0.21 to 0.508. Since γ < 1, it can be seen that the internal circular arc thread has a relatively small C... n and larger h n Smaller C n This means that the average thickness of the internal arc thread teeth is smaller, plus a larger h n This makes the internal circular arc thread teeth more slender, resulting in lower stiffness. When the internal and external circular arc threads interact, the internal circular arc thread teeth are more prone to bending deformation. When the internal and external circular arc threads are subjected to alternating loads, the internal circular arc thread teeth can absorb inertial forces through bending deformation, thereby reducing the bending deformation of the external circular arc thread teeth, improving the fatigue fracture resistance of the external circular arc thread, and enhancing its fatigue performance. Of course, too small a C... n and an excessively large h n This also means that if the inner arc thread teeth are too slender, the stiffness of the inner arc thread teeth will be too small, which will result in a significant decrease in the static load bearing capacity of the inner arc thread. Experimental verification shows that only when γ is in the appropriate range of 0.21~0.508 can the inner arc thread have sufficient static load bearing capacity, while the outer arc thread has good fatigue performance.

[0009] Furthermore, let P2 be the pitch of the inner circular arc thread and P1 be the pitch of the outer circular arc thread, then P2 = (1~1.0094)P1.

[0010] Furthermore, P2 = (1.0015~1.0079)P1.

[0011] Furthermore, defining the pitch of the internal circular arc thread as P2, then h n = (0.28~0.54)P2.

[0012] Furthermore, defining the pitch of the internal circular arc thread as P2, then 0.1P2≤C n ≤0.175P2.

[0013] Furthermore, the straight segments on the internal and external tooth flanks are in close contact, and the tooth height of the external circular arc thread is defined as h. w If the minor diameter is d1 and the minor diameter of the internal circular arc thread is D1, then .

[0014] Furthermore, the intersection of the straight segments on the inner flank and the inner crest contacts the outer root arc. Let the radius of the outer root arc be R1, the minor diameter of the inner arc thread be D1, and the minor diameter of the outer arc thread be d1. .

[0015] To achieve the above objectives, the internal circular arc thread in this invention adopts the following technical solution:

[0016] An internal circular arc thread, the thread profile of which includes, in sequence, an internal thread root arc, an internal thread flank straight segment, an internal thread crest straight segment, and an internal thread flank straight segment, wherein the width of the internal thread crest straight segment is defined as C. n The tooth height of the internal circular arc thread is h. n The slenderness ratio of the inner circular arc thread teeth is... The value of γ ranges from 0.21 to 0.508.

[0017] The beneficial effects of the above technical solution are as follows: This invention is an improved invention, further limiting the width C of the straight segment of the internal tooth crest. n tooth height h of the internal circular arc thread n The ratio of the two values ​​constitutes the slenderness ratio γ of the internal circular arc thread, and the value of γ ranges from 0.21 to 0.508. Since γ < 1, it can be seen that the internal circular arc thread has a relatively small C... n and larger h n Smaller C n This means that the average thickness of the internal arc thread teeth is smaller, plus a larger h nThis makes the internal circular arc thread teeth more slender, resulting in lower stiffness. When the internal and external circular arc threads interact, the internal circular arc thread teeth are more prone to bending deformation. When the internal and external circular arc threads are subjected to alternating loads, the internal circular arc thread teeth can absorb inertial forces through bending deformation, thereby reducing the bending deformation of the external circular arc thread teeth, improving the fatigue fracture resistance of the external circular arc thread, and enhancing its fatigue performance. Of course, too small a C... n and an excessively large h n This also means that if the inner arc thread teeth are too slender, the stiffness of the inner arc thread teeth will be too small, which will result in a significant decrease in the static load bearing capacity of the inner arc thread. Experimental verification shows that only when γ is in the appropriate range of 0.21~0.508 can the inner arc thread have sufficient static load bearing capacity, while the outer arc thread has good fatigue performance.

[0018] Furthermore, if the pitch of the internal circular arc thread is defined as P2, then P2 = (1~1.0094)P1, where P1 is the pitch of the external circular arc thread that is adapted to the internal circular arc thread.

[0019] Furthermore, P2 = (1.0015~1.0079)P1.

[0020] Furthermore, defining the pitch of the internal circular arc thread as P2, then h n = (0.28~0.54)P2.

[0021] Furthermore, defining the pitch of the internal circular arc thread as P2, then 0.1P2≤C n ≤0.175P2.

[0022] To achieve the above objectives, the nut in this invention adopts the following technical solution:

[0023] A nut has an internal circular arc thread. The thread profile includes, in sequence, an internal thread root arc, an internal thread flank straight segment, an internal thread crest straight segment, and an internal thread flank straight segment. The width of the internal thread crest straight segment is defined as C. n The tooth height of the internal circular arc thread is h. n The slenderness ratio of the inner circular arc thread teeth is... The value of γ ranges from 0.21 to 0.508.

[0024] The beneficial effects of the above technical solution are as follows: This invention is an improved invention, further limiting the width C of the straight segment of the internal tooth crest. n tooth height h of the internal circular arc thread n The ratio of the two values ​​constitutes the slenderness ratio γ of the internal circular arc thread, and the value of γ ranges from 0.21 to 0.508. Since γ < 1, it can be seen that the internal circular arc thread has a relatively small C... n and larger hn Smaller C n This means that the average thickness of the internal arc thread teeth is smaller, plus a larger h n This makes the internal circular arc thread teeth more slender, resulting in lower stiffness. When the internal and external circular arc threads interact, the internal circular arc thread teeth are more prone to bending deformation. When the internal and external circular arc threads are subjected to alternating loads, the internal circular arc thread teeth can absorb inertial forces through bending deformation, thereby reducing the bending deformation of the external circular arc thread teeth, improving the fatigue fracture resistance of the external circular arc thread, and enhancing its fatigue performance. Of course, too small a C... n and an excessively large h n This also means that if the inner arc thread teeth are too slender, the stiffness of the inner arc thread teeth will be too small, which will result in a significant decrease in the static load bearing capacity of the inner arc thread. Experimental verification shows that only when γ is in the appropriate range of 0.21~0.508 can the inner arc thread have sufficient static load bearing capacity, while the outer arc thread has good fatigue performance.

[0025] Furthermore, if the pitch of the internal circular arc thread is defined as P2, then P2 = (1~1.0094)P1, where P1 is the pitch of the external circular arc thread that is adapted to the internal circular arc thread.

[0026] Furthermore, P2 = (1.0015~1.0079)P1.

[0027] Furthermore, defining the pitch of the internal circular arc thread as P2, then h n = (0.28~0.54)P2.

[0028] Furthermore, defining the pitch of the internal circular arc thread as P2, then 0.1P2≤C n ≤0.175P2. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the tooth profile of the external circular arc thread in Embodiment 1 of the circular arc threaded connection pair of the present invention;

[0030] Figure 2 This is a schematic diagram of the tooth profile of the inner circular arc thread in Embodiment 1 of the circular arc threaded connection pair of the present invention;

[0031] Figure 3 This is a schematic diagram of the tooth profile fit between the inner and outer circular arc threads in Embodiment 1 of the circular arc threaded connection pair of the present invention.

[0032] Figure 4 This is a schematic diagram showing the calibration position of the external circular arc thread in Embodiment 1 of the circular arc threaded connection pair of the present invention;

[0033] Figure 5The graph shows the average stress versus time curves at the calibrated positions under alternating loads for thread pairs 1, 2, 3, 4, and 5 in Embodiment 1 of the circular arc threaded connection pair of the present invention, as well as the external circular arc thread in comparative thread pair 1.

[0034] Figure 6 This refers to the load ratio of each thread turn of the external circular arc thread used in conjunction with internal circular arc threads of different pitches under alternating loads when the slenderness ratio γ = 0.577 in the first embodiment of the circular arc thread connection pair of the present invention.

[0035] Figure 7 This refers to the load ratio of each turn of the external circular arc thread used in conjunction with internal circular arc threads of different pitches under alternating loads in a first embodiment of the circular arc thread connection pair of the present invention when the slenderness ratio γ = 0.341.

[0036] Figure 8 The load ratio of each thread turn of the external circular arc thread used in the first embodiment of the circular arc thread connection pair of the present invention to cooperate with the internal circular arc threads with different slenderness ratios and different pitches under alternating loads.

[0037] Figure 9 This is a schematic diagram of the tooth profile fit between the inner and outer circular arc threads in Embodiment 2 of the circular arc threaded connection pair of the present invention;

[0038] Figure 10 The graph shows the average stress versus time curves at the calibrated positions of thread pairs 7, 8, 9, 10, and 11 in Embodiment 2 of the circular arc threaded connection pair of the present invention, as well as the external circular arc thread in comparative thread pair 3, under alternating load.

[0039] Figure 11 This refers to the load ratio of each thread turn of the external circular arc thread used in conjunction with internal circular arc threads of different pitches under alternating loads when the slenderness ratio γ = 0.577 in the second embodiment of the circular arc thread connection pair of the present invention.

[0040] Figure 12 This refers to the load ratio of each turn of the external circular arc thread used in conjunction with internal circular arc threads of different pitches under alternating loads in Embodiment 2 of the circular arc thread connection pair of the present invention when the slenderness ratio γ = 0.341.

[0041] Figure 13 This refers to the load ratio of each turn of the external circular arc thread used in the second embodiment of the circular arc thread connection pair of the present invention, which is used in conjunction with internal circular arc threads with different slenderness ratios and different pitches, under alternating loads.

[0042] In the diagram: 1. External circular arc thread; 11. External thread crest; 12. External thread flank straight section; 13. External thread root arc; 2. Internal circular arc thread; 21. Internal thread root arc; 22. Internal thread flank straight section; 23. Internal thread crest straight section. Detailed Implementation

[0043] To address the technical problems existing in the prior art, the basic concept of this invention is to define the width C of the straight segment at the crest of the internal tooth. n tooth height h of the internal circular arc thread n When the ratio γ is within a suitable range, the circular arc thread teeth are relatively slender, and the stiffness of the inner circular arc thread teeth is relatively small. When the inner and outer circular arc thread teeth interact, the inner circular arc thread teeth are more prone to bending deformation. When the inner and outer circular arc threads are subjected to alternating loads, the inner circular arc thread teeth can absorb inertial forces through bending deformation, thereby reducing the bending deformation of the outer circular arc thread teeth, improving the fatigue fracture resistance of the outer circular arc thread, and improving the fatigue performance of the outer circular arc thread.

[0044] The features and performance of the present invention will be further described in detail below with reference to the embodiments.

[0045] Embodiment 1 of the circular arc threaded connection pair in this invention:

[0046] like Figure 4 As shown, the circular arc threaded connection pair includes a mating outer circular arc thread 1 and an inner circular arc thread 2. The outer circular arc thread 1 is provided on the bolt or stud, and the inner circular arc thread 2 is provided on the nut. Therefore, the circular arc threaded connection pair can be a common bolt connection pair including a bolt and a nut, a high-strength bolt connection pair including a bolt, a nut and a washer, or a stud pair including a stud and nuts at both ends.

[0047] like Figure 1 As shown, the tooth profile of the external circular arc thread 1 includes, in sequence, an external thread crest 11, an external thread flank straight segment 12 located on one side of the external thread root arc 13, an external thread root arc 13, and an external thread flank straight segment 12 located on the other side of the external thread root arc 13. In this embodiment, the external thread crest 11 is arc-shaped, and the external thread flank straight segment 12 is tangent to both the external thread crest 11 and the external thread root arc 13. In other embodiments, the external thread crest 11 may also extend in a straight line, in which case the external thread flank straight segment 12 is only tangent to the external thread root arc 13.

[0048] The two adjacent external thread flank segments 12 are symmetrical, and the included angle α between the two adjacent external thread flank segments 12 is the thread profile angle of the external circular arc thread. The range of α is 40°~80°, and it is generally preferred to be 60°. In addition, the pitch of the external circular arc thread is P1, the minor diameter is d1, the major diameter is d, the radius of the external thread root arc 13 is R1, the radius of the external thread crest 11 is R2, and the thread height of the external circular arc thread is h. wIn fact, the structure of the external circular arc thread is existing technology, and this invention does not improve the external circular arc thread.

[0049] like Figure 2 As shown, the tooth profile of the internal circular arc thread 2 includes, in sequence, an internal root arc 21, an internal flank straight segment 22 on one side of the internal crest straight segment 23, an internal crest straight segment 23, and an internal flank straight segment 22 on the other side of the internal crest straight segment 23, wherein the internal flank straight segment 22 is tangent to the internal root arc 21. Two adjacent internal flank straight segments 22 are symmetrical, and the included angle β between two adjacent internal flank straight segments 22 is the tooth profile angle of the internal circular arc thread. Furthermore, the pitch of the internal circular arc thread is P2, the minor diameter is D1, the major diameter is D, and the width of the internal crest straight segment 23 is C. n The radius of the internal thread root arc 21 is r, and the thread height of the internal arc thread is h. n .

[0050] like Figure 3 As shown, in this embodiment, β=α, and the inner thread side straight segment 22 and the outer thread side straight segment 12 are in close contact. To ensure a certain contact area between the inner and outer circular arc threads, and a certain overlap rate between the inner and outer circular arc thread teeth, and to avoid the inner and outer circular arc thread teeth from disengaging due to an excessively small overlap rate, this embodiment limits... That is, the distance between the straight segment 23 of the internal thread crest and the root of the external arc thread cannot exceed half the height of the external arc thread. Of course, in other embodiments... It can also be less than 0.49, 0.48, 0.47, 0.51, 0.52 or 0.53.

[0051] In this invention, the slenderness ratio of the internal circular arc thread is defined as γ, where γ is the width C of the straight segment at the crest of the internal thread. n tooth height h of the internal circular arc thread n The ratio, i.e. The value of γ ranges from 0.21 to 0.508. From this range, it can be seen that γ < 1 and the internal circular arc thread has a smaller C value. n and larger h n Smaller C n This means that the average thickness of the internal arc thread teeth is smaller, plus a larger h n This makes the inner arc thread teeth more slender, resulting in lower stiffness. When the inner and outer arc threads interact, the inner arc thread teeth are more prone to bending deformation. When the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb inertial forces through bending deformation, thereby reducing the bending deformation of the outer arc thread teeth, improving the fatigue fracture resistance of the outer arc thread teeth, and enhancing the fatigue performance of the outer arc thread teeth.

[0052] Of course, a C that is too small nand an excessively large h n This also means that if the inner arc thread teeth are too slender, the stiffness of the inner arc thread teeth will be too small, which will result in a significant decrease in the static load bearing capacity of the inner arc thread. Experimental verification shows that only when γ is in the appropriate range of 0.21~0.508 can the inner arc thread have sufficient static load bearing capacity, while the outer arc thread has good fatigue performance.

[0053] Furthermore, while ensuring that the value of γ is within the range of 0.21 to 0.508, this embodiment limits h. n = (0.28~0.54)P2, 0.1P2≤C n ≤0.175P², where C is determined for practical engineering applications. n and h n The specific value provides a basis. Of course, in other embodiments, as long as the range of γ can be guaranteed to be 0.21~0.508, C... n and h n The value of is not limited to the range mentioned above.

[0054] Furthermore, as in Example 1, the pitches of the internal and external circular arc threads are equal, i.e., P1=P2. To verify the superiority of the circular arc thread connection pair in this example, six thread pair structures are given below, with specific thread parameters shown in Table 1. Among them, thread pair 1 is an existing circular arc thread connection pair, and the tooth profiles of its internal and external circular arc threads are both existing technologies. The slenderness ratio γ of the internal circular arc thread is greater than 0.508. The main difference between thread pair 1, thread pair 2, thread pair 3, thread pair 4, and thread pair 5 lies in the different slenderness ratio γ of the internal circular arc thread. The slenderness ratio γ of the internal circular arc thread of thread pair 1, thread pair 2, thread pair 3, and thread pair 4 is between 0.21 and 0.508, while the slenderness ratio γ of the internal circular arc thread of thread pair 5 is less than 0.21.

[0055] Table 1. Specific thread parameters of Example 1 in Implementation Method 1

[0056]

[0057] Based on the above parameters, tensile strength tests were conducted on the bolts and nuts. Specifically, a fixed constraint was applied to the nut, and an increasing tensile force was applied to the bolt. The tensile strength of the bolts corresponding to different thread pairs was measured, as shown in Table 2. For bolts with the same thread parameters, three samples were used for testing.

[0058] Table 2. Tensile strength of bolts corresponding to each threaded pair in Example 1 of Embodiment 1.

[0059]

[0060] As can be seen from the results in Table 2, the overall tensile strength of the bolts corresponding to threaded pairs 1, 2, 3, and 4 is at the same level. However, the slenderness ratio of the inner arc thread of the nut corresponding to threaded pair 5 is too small. Under load, the inner arc thread teeth undergo large bending deformation. When the load force is far less than that of other bolts, the bolt and nut will disengage. This indicates that the deformation of the inner arc thread teeth is too large and the static load bearing capacity is extremely poor.

[0061] Simultaneously, based on the thread parameters in Table 1, this invention also employs general-purpose finite element analysis software to perform dynamic analysis on the internal and external circular arc threads. Specifically, a fixed constraint is applied to the nut, and an alternating load varying with time is applied to the bolt or stud. This yields the results under the same alternating load, showing the external circular arc thread in the six thread pairs at the calibrated position (calibrated position is...). Figure 4 The curve showing the average stress versus time at the red location (the first thread of the external arc thread, which is usually also the location of the highest stress concentration) is shown in the image. Figure 5 As shown.

[0062] from Figure 5 As can be seen, at each loading moment, the average stress of the outer circular arc thread in thread pair 1 to thread pair 5 at the calibration position is less than that of the outer circular arc thread in thread pair 1 at the calibration position. Furthermore, the average stress of the outer circular arc thread in thread pair 5 at the calibration position is always the smallest. The stress increases sequentially for thread pair 4, thread pair 3, thread pair 2, and thread pair 1, indicating that as the slenderness ratio γ gradually decreases, the average stress of the outer circular arc thread at the calibration position gradually decreases. This confirms that the slenderer the inner circular arc thread, the lower its stiffness and the easier it is for it to bend and deform. Therefore, when the inner and outer circular arc threads are subjected to alternating loads, the inner circular arc thread can absorb more inertial force through bending deformation, reducing the bending deformation of the outer circular arc thread and improving its fatigue performance.

[0063] Of course, the tensile strength test results above show that the bolts and nuts in threaded pair 5 experienced stripping, making it unusable in practical engineering. Therefore, based on the results in Table 2, and assuming that the overall tensile strength of the bolts corresponding to threaded pairs 1, 2, 3, and 4 are at the same level, combined with... Figure 5 It can be seen that thread pair 4 is optimal. That is, under the premise of ensuring that the inner arc thread has sufficient static load bearing capacity, the smaller the slenderness ratio γ of the inner arc thread, the more significant the effect of improving the fatigue performance of the outer arc thread.

[0064] In addition, in order to compare the effect of unequal pitch on the fatigue performance of external circular arc threads, this embodiment also provides an embodiment 2. In embodiment 2, the pitch P2 of the internal circular arc thread is greater than the pitch P1 of the external circular arc thread, specifically P2 = (1~1.0094)P1, preferably P2 = (1.0015~1.0079)P1.

[0065] According to existing research, when internal and external threads of equal pitch are subjected to load, the external thread is subjected to tensile elongation, while the internal thread is subjected to compressive force. The external thread near the support surface (taking bolts and nuts as an example, the support surface is the end face of the nut used to clamp the connected parts) elongates more, while the external thread far from the support surface elongates less. This results in the axial load of the threaded connection being mainly borne by the first three turns (i.e., the first three threads) of the thread closest to the support surface, while the subsequent threads are almost unloaded. This causes a significant stress concentration phenomenon in the first three turns of the thread, with the first turn bearing the largest load, followed by the second turn, and the third turn bearing the smallest load.

[0066] Based on this, in this embodiment, the pitch P2 of the inner arc thread is designed to be greater than the pitch P1 of the outer arc thread. This allows the inner and outer arc threads to make contact preferentially at a point far from the connected parts (i.e., far from the support surface). Subsequently, as the load increases to the rated preload, the inner and outer arc thread teeth can make contact one by one. This can effectively improve the load uniformity of each thread tooth under the rated preload. Therefore, when the inner and outer arc threads are subjected to alternating loads with an average load of rated preload, the meshing length of the inner and outer arc threads changes with the load, preventing obvious load concentration on a certain thread.

[0067] Meanwhile, for internal circular arc threads with a slenderness ratio γ in the range of 0.21 to 0.508, the stiffness of the internal circular arc thread teeth is relatively small, making them prone to bending deformation. If internal and external circular arc threads with equal pitch are still used for mating, the first thread will bear the greatest load, but the stiffness of the internal circular arc thread teeth is insufficient, making tooth breakage very likely. After the first internal circular arc thread tooth breaks, the second thread tooth begins to bear the load and faces the same problem, eventually leading to complete disengagement of the bolt and nut. However, by designing the pitch P2 of the internal circular arc thread to be greater than the pitch P1 of the external circular arc thread, the load uniformity of each thread tooth is improved. That is, when the internal and external circular arc threads are subjected to alternating loads, each thread tooth is stressed simultaneously, and the load is no longer concentrated on the first three threads. Therefore, even though the internal circular arc thread teeth have relatively small stiffness and are prone to bending deformation, the normal use of the bolt and nut can still be guaranteed.

[0068] Of course, the pitch P2 of the internal circular arc thread should not be too large and should be within a suitable range. Otherwise, if the internal and external circular arc threads make priority contact at the point away from the connected part (i.e. away from the support surface), as the load gradually increases, the subsequent threads will not be able to make effective contact one by one. Instead, the threads at the point away from the connected part (i.e. away from the support surface) will be subjected to excessive force, which is the same effect as the first thread with medium pitch in the prior art bearing too much load. This is not the result that this invention wants.

[0069] Experiments have shown that when P2 = (1~1.0094)P1, it can not only effectively improve the load-bearing ratio of each thread and enhance the fatigue performance of the outer arc thread, but also solve the problem of insufficient load-bearing capacity caused by the excessively slender inner arc thread.

[0070] To verify the superiority of this embodiment, comparative experiments were conducted as shown in Table 3. This embodiment retains the comparative thread pair 1, thread pair 2, and thread pair 3, while introducing comparative thread pair 2 and thread pair 6. The only difference between comparative thread pair 1 and comparative thread pair 2 is the pitch of the inner arc thread. Since P1 = 6.35, then P2 = (1~1.0094)P1 = 6.35~6.41. The preferred range of P2 is (1.0015~1.0079)P1 = 6.36~6.4. Therefore, the pitch of the inner arc thread of comparative thread pair 1 is exactly at the end value and is not within the preferred range, while the pitch of the inner arc thread of comparative thread pair 2 is within the preferred range.

[0071] Table 3 Specific thread parameters of Example 2 in Implementation Method 1

[0072]

[0073] Secondly, the difference between threaded pair 2 and threaded pair 6 is that the pitch of the inner and outer circular arc threads in threaded pair 2 is equal, while the pitch of the inner circular arc thread in threaded pair 6 is within the preferred range. Meanwhile, the slenderness ratio γ of the inner circular arc threads in both threaded pair 2 and threaded pair 6 is in the range of 0.21 to 0.508.

[0074] One of the similarities between thread pair 2 and thread pair 6 is that the pitch of the internal circular arc thread is within the preferred range. The difference is that the slenderness ratio γ of the internal circular arc thread in thread pair 6 is in the range of 0.21~0.508, while the slenderness ratio γ of the internal circular arc thread in thread pair 2 is greater than 0.508.

[0075] The pitch of the inner circular arc thread of thread pair 1 is also an end value and is not within the preferred range, but the slenderness ratio γ of the inner circular arc thread is 0.508.

[0076] Based on the above parameters, fatigue tests were conducted on the bolts and nuts. Table 4 shows the number of cycles for comparative thread pair 1, comparative thread pair 2, thread pair 2, and thread pair 6 under the same load on the same fatigue test equipment.

[0077] Table 4 Number of fatigue cycles

[0078]

[0079] As shown in Table 4, thread pair 1, with its existing circular arc thread structure, has the lowest fatigue life. Thread pair 2, based on the existing circular arc thread, has an improved fatigue life because the pitch P2 of the internal circular arc thread is within the preferred range. In thread pair 2, the slenderness ratio γ of the internal circular arc thread is between 0.21 and 0.508, resulting in a significantly higher number of fatigue cycles compared to the existing circular arc thread profile. In thread pair 6, the pitch P2 of the internal circular arc thread is within the preferred range, and the slenderness ratio γ is between 0.21 and 0.508, resulting in the highest number of fatigue cycles, consistent with the previous theoretical analysis.

[0080] It should be noted that, as shown in Table 4, for the comparative thread pairs 1, 1, and 2 with equal pitches of the internal circular arc threads (P2 is 6.35 for all pairs), the fatigue life of the connection pairs continuously increases as the slenderness ratio γ of the internal circular arc threads decreases. Among them, the slenderness ratio corresponding to the comparative thread pair 1 is 0.577, which has the worst fatigue life compared to the other connection pairs, so it is discarded. Therefore, the upper limit of the slenderness ratio γ is determined to be 0.508. Of course, for the comparative thread pairs 2 and 6 with equal pitches of the internal circular arc threads (P2 is 6.38 for all pairs), although the slenderness ratio γ of the internal circular arc thread in the comparative thread pair 2 is 0.577, exceeding the optimal range, the fatigue cycle number is not low because the pitch P2 is within the preferred range.

[0081] Since the concept of this embodiment is to improve the load uniformity of each thread of the external circular arc thread by changing the pitch of the internal circular arc thread, while reducing the maximum load of the thread, the load ratio of each thread of the external circular arc thread used with internal circular arc threads of different pitches under alternating loads was investigated next, under the condition of the same slenderness ratio γ.

[0082] First, the pitch P1 of the external circular arc thread was defined as 6.35 mm, and the minor diameter d1 as 30.6 mm. The slenderness ratio γ of the internal circular arc thread was 0.577, and the minor diameter D1 was 32.2 mm. The pitch P2 of several internal circular arc threads were 6.35 mm, 6.36 mm, 6.38 mm, 6.40 mm, 6.41 mm, and 6.42 mm, respectively. Dynamic analysis of the internal and external circular arc threads was performed using general-purpose finite element analysis software. Specifically, a fixed constraint was applied to the nut, and a time-varying alternating load was applied to the bolt or stud. Under the same alternating load, Figure 6 The figure shows the load ratio of each thread turn of the external circular arc thread used with different pitch internal circular arc threads at a loading time of 0.0025s. It can be seen from the figure that when P2=6.42mm, that is, when P2>6.41mm, the load uniformity of each thread turn of the external circular arc thread is not only very poor, but the load ratio of the seventh turn is also higher than the maximum load ratio in the prior art (P2=6.35mm). Considering that the maximum load ratio when P2=6.41mm does not exceed the maximum load ratio in the prior art (P2=6.35mm), the upper limit of P2 is chosen to be 6.41mm, which corresponds to the range of P2 defined above as (1~1.0094)P1.

[0083] At the same time from Figure 6 It can also be seen that when P2 is 6.36mm, 6.38mm, and 6.40mm, the load uniformity of each ring is better than that of the end values ​​(P2 is 6.35mm and 6.41mm), which corresponds to the preferred range of P2 defined above as (1.0015~1.0079)P1.

[0084] Secondly, this embodiment also provides the thread load ratio of each turn of the external circular arc thread used with internal circular arc threads of different pitches under alternating loads when the slenderness ratio γ = 0.341. Figure 7 As shown, when P2 = 6.42 mm, that is, when P2 > 6.41 mm, the load uniformity of each thread in the external arc thread is not only very poor, but the load ratio of the seventh thread is also higher than the maximum load ratio in the prior art (P2 = 6.35 mm). Considering that the maximum load ratio at P2 = 6.41 mm does not exceed the maximum load ratio in the prior art (P2 = 6.35 mm), the upper limit of P2 is chosen to be 6.41 mm, corresponding to the previously defined range of P2 as (1~1.0094)P1. Meanwhile, from... Figure 7 It can also be seen that when P2 is 6.36mm, 6.38mm, and 6.40mm, the load uniformity of each ring is better than that of the end values ​​(P2 is 6.35mm and 6.41mm), which corresponds to the preferred range of P2 defined above as (1.0015~1.0079)P1.

[0085] Therefore, combining Figure 6 and Figure 7 It can be seen that even if the slenderness ratio γ is different, the variation law of the thread load ratio of each turn of the external circular arc thread used with the internal circular arc thread with different pitches is the same. Under different values ​​of slenderness ratio γ, the range and preferred range of the pitch P2 of the internal circular arc thread are the same.

[0086] Furthermore, such as Figure 8 The figure shows the load ratio of each turn of the external circular arc thread used with internal circular arc threads of different slenderness ratios and pitches under alternating loads. It can be seen from the figure that when the slenderness ratio γ of the internal circular arc thread is 0.577 and is not in the range of 0.21~0.508, the external circular arc thread with a larger pitch P2 (P2=6.38mm, within the preferred range) has better load uniformity. This proves that even if the slenderness ratio γ is not preferred, simply increasing the pitch of the internal circular arc thread can improve the load uniformity of each turn of the external circular arc thread.

[0087] When the pitch P2 of the internal circular arc thread is 6.35 mm, the external circular arc thread corresponding to the internal circular arc thread with a smaller slenderness ratio γ (γ=0.341, in the range of 0.21~0.508) has better load uniformity in each turn. This proves that when the pitches of the internal and external circular arc threads are equal, reducing the slenderness ratio γ of the internal circular arc thread alone can also improve the load uniformity in each turn of the external circular arc thread.

[0088] When the slenderness ratio γ of the internal circular arc thread is 0.341 and is within the range of 0.21 to 0.508, the external circular arc thread corresponding to the internal circular arc thread with a larger pitch P2 (P2=6.38mm, within the preferred range) has better load uniformity in each turn and is the best among several threads. This proves that the load uniformity in each turn of the external circular arc thread is improved the most after the slenderness ratio γ and pitch P2 are combined.

[0089] Embodiment 2 of the circular arc threaded connection pair in this invention:

[0090] The difference between Embodiment 2 and Embodiment 1 lies in the contact position of the internal and external circular arc threads. In Embodiment 2, for example... Figure 9 As shown, line segment AB is the external thread side straight line segment 12, and point B is the tangent point between the external thread side straight line segment 12 and the external thread root arc 13. The intersection of the internal thread side straight line segment 22 and the internal thread crest straight line segment 23 contacts the external thread root arc 13, and the contact point is C. Compared with Embodiment 1, in Embodiment 2, the contact point of the internal and external arc threads is closer to the root of the external arc thread. In the figure, B' is the tangent point between the external thread root arc 13 and the other external thread side straight line segment, and the internal thread crest straight line segment 23 is located on the side of BB' closer to the external arc thread axis.

[0091] To ensure proper contact between the internal and external circular arc threads structurally, with the contact point located on the external thread root arc 13, the width C of the internal thread crest straight segment 23 must be guaranteed. n ≤CC', where C is the contact point of the internal and external circular arc threads, and C' is the intersection of the extension of the internal crest line segment 23 and the external root arc 13; otherwise, if C n If the internal thread crest straight segment 23 cannot be accommodated between CC', the internal and external circular arc threads cannot be mated.

[0092] Additionally, point O in the diagram is the center of the external thread root arc 13. OE is perpendicular to the axis of the external thread arc. Point E lies on the external thread root arc 13. OE is perpendicular to CC', and OE intersects CC' at point F. OC = OE = R1. Based on geometric relationships, we know that: ,so .

[0093] To verify the superiority of the circular arc threaded connection pair in Embodiment 2, six threaded connection structures are given below. The specific thread parameters are shown in Table 5. The difference between Embodiment 2 and Embodiment 1 (Table 1) is that the minor diameter D1 of the internal circular arc thread is different. The minor diameter D1 of the internal circular arc thread in Embodiment 2 is smaller, so that the intersection of the straight section of the internal tooth side and the straight section of the internal tooth crest can contact the circular arc of the external tooth root.

[0094] Table 5 Specific thread parameters in Implementation Method 2

[0095]

[0096] Based on the above parameters, tensile strength tests were conducted on the bolts and nuts. Specifically, a fixed constraint was applied to the nut, and an increasing tensile force was applied to the bolt. The tensile strength of the bolts corresponding to different thread pairs was measured, as shown in Table 6.

[0097] Table 6 Tensile strength of bolts corresponding to each threaded pair in Implementation Method 2

[0098]

[0099] In the second implementation method, since the intersection of the straight section of the inner tooth side and the straight section of the inner tooth top contacts the arc of the outer tooth root, the overlap rate between the inner and outer threads increases, and the load-bearing capacity of the threads increases. Therefore, no stripping phenomenon occurs between the bolt and the nut. Even the thread pair 11 with the smallest slenderness ratio γ does not experience stripping phenomenon.

[0100] Meanwhile, based on the thread parameters in Table 5, a dynamic analysis of the internal and external circular arc threads was performed using general-purpose finite element analysis software. Specifically, a fixed constraint was applied to the nut, and an alternating load varying with time was applied to the bolt or stud. The average stress versus time curves of the external circular arc threads in the six thread pairs at the calibrated position (the calibrated position is the same as above) under the same alternating load were obtained, as shown below. Figure 10 As shown.

[0101] from Figure 10 As can be seen, at each loading moment, the average stress of the outer circular arc threads in thread pairs 7 to 11 at the calibration position is less than that of the outer circular arc threads in the comparative thread pair 3 at the calibration position, and the average stress of the outer circular arc threads in thread pair 11 at the calibration position is always the minimum. As the slenderness ratio γ gradually decreases, the average stress of the outer circular arc threads at the calibration position gradually decreases, confirming that the slenderer the inner circular arc thread, the lower its stiffness, and the more easily it undergoes bending deformation. Therefore, when the inner and outer circular arc threads are subjected to alternating loads, the inner circular arc thread can absorb more inertial force through bending deformation, reducing the bending deformation of the outer circular arc thread and improving its fatigue performance.

[0102] Of course, the tensile strength test above shows that, under the premise that the overall tensile strength of the bolts corresponding to threaded pairs 7 to 11 and the comparative threaded pair 3 is at the same level, threaded pair 11 is the best. That is, under the premise that the inner arc thread has sufficient static load bearing capacity, the smaller the slenderness ratio γ of the inner arc thread, the more significant the effect of the outer arc thread on improving the fatigue performance of the outer arc thread.

[0103] Furthermore, this embodiment also explores the thread load ratio of each turn of the external circular arc thread used with internal circular arc threads of different pitches under alternating loads, when the slenderness ratio γ is the same.

[0104] First, when the slenderness ratio γ of the internal circular arc thread is 0.577 and the minor diameter D1 is 31.5 mm, and the pitch P1 of the external circular arc thread is 6.35 mm and the minor diameter d1 is 30.6 mm, the pitch P2 of the various internal circular arc threads are 6.35 mm, 6.36 mm, 6.38 mm, 6.40 mm, 6.41 mm, and 6.42 mm, respectively. A general-purpose finite element analysis software is used to perform dynamic analysis on the internal and external circular arc threads. Specifically, a fixed constraint is applied to the nut, and a time-varying alternating load is applied to the bolt or stud. Under the same alternating load, Figure 11The figure shows the load ratio of each thread turn of the external circular arc thread used with different pitch internal circular arc threads at a loading time of 0.0025s. It can be seen from the figure that when P2=6.42mm, that is, when P2>6.41mm, the load uniformity of each thread turn of the external circular arc thread is not only very poor, but the load ratio of the seventh turn is also higher than the maximum load ratio in the prior art (P2=6.35mm). Considering that the maximum load ratio when P2=6.41mm does not exceed the maximum load ratio in the prior art (P2=6.35mm), the upper limit of P2 is chosen to be 6.41mm, which corresponds to the range of P2 defined above as (1~1.0094)P1.

[0105] At the same time from Figure 11 It can also be seen that when P2 is 6.36mm, 6.38mm, and 6.40mm, the load uniformity of each ring is better than that of the end values ​​(P2 is 6.35mm and 6.41mm), which corresponds to the preferred range of P2 defined above as (1.0015~1.0079)P1.

[0106] This embodiment also provides the thread load ratio of each turn of the external circular arc thread used with internal circular arc threads of different pitches under alternating loads when the slenderness ratio γ = 0.341. Figure 12 As shown, when P2 = 6.42 mm, that is, when P2 > 6.41 mm, the load uniformity of each thread in the external arc thread is not only very poor, but the load ratio of the seventh thread is also higher than the maximum load ratio in the prior art (P2 = 6.35 mm). Considering that the maximum load ratio at P2 = 6.41 mm does not exceed the maximum load ratio in the prior art (P2 = 6.35 mm), the upper limit of P2 is chosen to be 6.41 mm, corresponding to the previously defined range of P2 as (1~1.0094)P1. Meanwhile, from... Figure 12 It can also be seen that when P2 is 6.36mm, 6.38mm, and 6.40mm, the load uniformity of each ring is better than that of the end values ​​(P2 is 6.35mm and 6.41mm), which corresponds to the preferred range of P2 defined above as (1.0015~1.0079)P1.

[0107] Therefore, combining Figure 11 and Figure 12 It can be seen that even if the slenderness ratio γ is different, the variation law of the thread load ratio of each turn of the external circular arc thread used with the internal circular arc thread with different pitches is the same. Under different values ​​of slenderness ratio γ, the range and preferred range of the pitch P2 of the internal circular arc thread are the same.

[0108] Furthermore, such as Figure 13The figure shows the load ratio of each turn of the external circular arc thread used with internal circular arc threads of different slenderness ratios and pitches under alternating loads. It can be seen from the figure that when the slenderness ratio γ of the internal circular arc thread is 0.577 and is not in the range of 0.21~0.508, the external circular arc thread with a larger pitch P2 (P2=6.38mm, within the preferred range) has better load uniformity. This proves that even if the slenderness ratio γ is not preferred, simply increasing the pitch of the internal circular arc thread can improve the load uniformity of each turn of the external circular arc thread.

[0109] When the pitch P2 of the internal circular arc thread is 6.35 mm, the external circular arc thread corresponding to the internal circular arc thread with a smaller slenderness ratio γ (γ=0.341, in the range of 0.21~0.508) has better load uniformity in each turn. This proves that when the pitches of the internal and external circular arc threads are equal, reducing the slenderness ratio γ of the internal circular arc thread alone can also improve the load uniformity in each turn of the external circular arc thread.

[0110] When the slenderness ratio γ of the internal circular arc thread is 0.341 and is within the range of 0.21 to 0.508, the external circular arc thread corresponding to the internal circular arc thread with a larger pitch P2 (P2=6.38mm, within the preferred range) has better load uniformity in each turn and is the best among several threads. This proves that the load uniformity in each turn of the external circular arc thread is improved the most after the slenderness ratio γ and pitch P2 are combined.

[0111] In other embodiments of the circular arc threaded connection pair: Unlike embodiments one and two, the tooth profile angles of the inner and outer circular arc threads may not be equal. For example, the tooth profile angle of the inner circular arc thread is smaller than that of the outer circular arc thread.

[0112] The implementation of the internal circular arc thread in this invention is as follows: the specific structure of the internal circular arc thread is the same as that of the internal circular arc thread in any of the above-mentioned implementations of the circular arc thread connection pair, and will not be repeated here.

[0113] The nut in this invention is provided with an inner arc thread. The specific structure of the inner arc thread is the same as that of the inner arc thread in any embodiment of the above-mentioned arc threaded connection pair, and will not be repeated here.

[0114] The above description is merely 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 determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A circular arc threaded connection pair, comprising mating internal and external circular arc threads, wherein the tooth profile of the internal circular arc thread includes, in sequence, an internal root arc, an internal flank straight segment on one side of the internal crest straight segment, an internal crest straight segment, and an internal flank straight segment on the other side of the internal crest straight segment; and the tooth profile of the external circular arc thread includes, in sequence, an external thread crest, an external flank straight segment on one side of the external root arc, an external root arc, and an external flank straight segment on the other side of the external root arc, characterized in that, a definition is provided. The width of the straight segment at the crest of the internal tooth is C. n The tooth height of the internal circular arc thread is h. n Then, the slenderness ratio of the internal circular arc thread teeth is defined as γ. The value of γ ranges from 0.341 to 0.

352.

2. The circular arc threaded connection pair according to claim 1, characterized in that, a definition is provided. The pitch of the internal circular arc thread is P2, and the pitch of the external circular arc thread is P1. Then P2 = (1.0016~1.0079)P1.

3. The circular arc threaded connection pair according to claim 2, characterized in that, P2 = (1.0047~1.0079)P1.

4. The circular arc threaded connection pair according to any one of claims 1 to 3, characterized in that, the definition is... If the pitch of the internal circular arc thread is P2, then h n = (0.28~0.54)P2.

5. The circular arc threaded connection pair according to any one of claims 1 to 3, characterized in that, Let P2 be the pitch of the internal circular arc thread, then 0.1P2≤C n ≤0.175P2.

6. The circular arc threaded connection pair according to any one of claims 1 to 3, characterized in that, The straight segments on the internal and external tooth flanks are in contact, and the tooth height of the external circular arc thread is defined as h. w If the minor diameter is d1 and the minor diameter of the internal circular arc thread is D1, then .

7. The circular arc threaded connection pair according to any one of claims 1 to 3, characterized in that, The intersection of the straight segments on the inner flank and the inner crest of the thread contacts the outer root arc. Let the radius of the outer root arc be R1, the minor diameter of the inner arc thread be D1, and the minor diameter of the outer arc thread be d1. .

8. An internal circular arc thread, the thread profile comprising, in sequence, an internal thread root arc, an internal thread flank straight segment on one side of the internal thread crest straight segment, an internal thread crest straight segment, and an internal thread flank straight segment on the other side of the internal thread crest straight segment, characterized in that, a definition is provided. The width of the straight segment at the crest of the internal tooth is C. n The tooth height of the internal circular arc thread is h. n Then, the slenderness ratio of the internal circular arc thread teeth is defined as γ. The value of γ ranges from 0.341 to 0.

352.

9. The internal circular arc thread according to claim 8, characterized in that, the definition is... If the pitch of the internal circular arc thread is P2, then P2 = (1.0016~1.0079)P1, where P1 is the pitch of the external circular arc thread that is compatible with the internal circular arc thread.

10. The internal circular arc thread according to claim 9, characterized in that, P2 = (1.0047~1.0079)P1.

11. The internal circular arc thread according to any one of claims 8 to 10, characterized in that, Define the pitch of the internal circular arc thread as P2, then h n = (0.28~0.54)P2.

12. The internal circular arc thread according to any one of claims 8 to 10, characterized in that, Let P2 be the pitch of the internal circular arc thread, then 0.1P2≤C n ≤0.175P2.

13. A nut having an internal circular arc thread, the thread profile comprising, in sequence, an internal thread root arc, an internal thread flank straight segment on one side of the internal thread crest straight segment, an internal thread crest straight segment, and an internal thread flank straight segment on the other side of the internal thread crest straight segment, characterized in that, the definition is... The width of the straight segment at the crest of the internal tooth is C. n The tooth height of the internal circular arc thread is h. n Then, the slenderness ratio of the internal circular arc thread teeth is defined as γ. The value of γ ranges from 0.341 to 0.

352.

14. The nut according to claim 13, characterized in that, the definition is... The pitch of the internal circular arc thread is P2, and the pitch of the external circular arc thread is P1. Then P2 = (1.0016~1.0079)P1.

15. The nut according to claim 14, characterized in that, P2 = (1.0047~1.0079)P1.

16. The nut according to any one of claims 13 to 15, characterized in that, Define the pitch of the internal circular arc thread as P2, then h n = (0.28~0.54)P2.

17. The nut according to any one of claims 13 to 15, characterized in that, Let P2 be the pitch of the internal circular arc thread, then 0.1P2≤C n ≤0.175P2.

Images