Arc thread connection pair, inner arc thread and nut

Abstract

The invention provides an arc thread connection pair, an inner arc thread and a nut, and belongs to the technical field of thread connection. The arc thread connection pair comprises an inner arc thread and an outer arc thread which are matched with each other, and the thread form of the inner arc thread comprises an inner thread bottom arc, an inner thread side linear section, an inner thread top linear section and an inner thread side linear section which are connected in sequence; the thread form of the outer arc thread comprises an outer thread crest, an outer thread side straight line section, an outer thread bottom arc and an outer thread side straight line section which are connected in sequence, the width of the inner thread crest straight line section is defined as Cn, the thread height of the inner arc thread is defined as hn, and the value range of the slenderness ratio # imgabs0 # gamma of the inner arc thread is 0.21-0.508. The inner arc thread teeth are slender, smaller in rigidity and easier to bend and deform, and when the inner arc thread and the outer arc thread bear alternating loads, the inner arc thread teeth can absorb inertia force through bending deformation, so that bending deformation of the outer arc thread teeth is reduced, and the fatigue performance of the outer arc thread is improved.

Description

Technical Field

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

[0002] Thread fatigue fracture is a critical technical challenge in engineering, particularly in equipment and components subjected to high stresses and long service lives. Existing threads are generally designed for static load safety, often with a larger internal thread thickness. For example, in metric and MJ threads, the average internal thread thickness is greater than that of the corresponding external thread. This results in greater stiffness for the internal thread than for the external thread. During load-bearing conditions, the internal thread exhibits minimal bending deformation, resulting in a strong load-bearing capacity and a low risk of stripping. However, excessive internal thread stiffness can reduce the fatigue performance of the external thread. This is because when the internal and external threads are subjected to alternating axial loads, the threads vibrate with the alternating loads. Due to their greater stiffness, the internal thread exhibits less bending deformation, while the corresponding external thread requires greater deformation to absorb the inertial force generated by the gradual load. This increases the bending moment on the external thread, significantly increasing the high stress generated at the root of the external thread and, in turn, the risk of fatigue fracture.

[0003] A Chinese utility model patent with authorization announcement number CN209818480U discloses a high-strength arc thread connection pair, which includes a bolt and a nut, wherein the bolt is provided with an external arc thread and the nut is provided with an internal arc thread. The thread profile of the external arc thread includes a sequentially connected external thread root arc (i.e., external thread root arc), an external thread flank straight line segment (i.e., external thread flank straight line segment), an external thread crest arc (i.e., external thread crest), and an external thread flank straight line segment, wherein the external thread flank straight line segment is tangent to the external thread root arc and the external thread crest arc, respectively. The thread profile of the internal arc thread includes a sequentially connected internal thread root arc (i.e., internal thread root arc), an internal thread flank straight line segment (i.e., internal thread flank straight line segment), an internal thread crest straight line segment (i.e., internal thread crest straight line segment), and an internal thread flank straight line segment, wherein the internal thread flank straight line segment is tangent to the internal thread root arc.

[0004] When the above-mentioned arc thread connection pair is in use, the straight section on the outer tooth side is in close contact with the straight section on the inner tooth side. A large arc structure is designed at the bottom of the outer arc thread to reduce the high stress concentration generated at the bottom of the outer arc thread. At the same time, the average tooth thickness of the inner arc thread is smaller than the average tooth thickness of the outer arc thread. These designs improve the fatigue performance of the outer arc thread to a certain extent, but the improvement effect is limited. The fatigue performance of the outer arc thread is still relatively poor, and fatigue fracture is prone to occur in actual use. Summary of the Invention

[0005] The purpose of the present invention is to provide a circular arc thread connection pair to solve the problem of poor fatigue performance of the external arc thread in the existing circular arc thread connection pair; the purpose of the present invention is also to provide an internal arc thread, which can improve the fatigue performance of the external arc thread when used in conjunction with the existing external arc thread; the purpose of the present invention is also to provide a nut, which can improve the fatigue performance of the external arc thread on the bolt or stud when used in conjunction with the existing bolt or stud.

[0006] To achieve the above objectives, the arc thread connection pair in the present invention adopts the following technical solutions:

[0007] A circular arc thread connection pair includes an internal arc thread and an external arc thread that cooperate with each other. The tooth profile of the internal arc thread includes an inner tooth bottom 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 external arc thread includes an outer thread top, an outer tooth side straight line segment, an outer tooth bottom 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 internal arc thread is h n , then the slenderness ratio of the internal arc thread tooth is The value range of γ is 0.21~0.508.

[0008] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further limits the width C of the inner tooth top straight line segment. n The tooth height h of the internal arc thread n The ratio of the inner arc thread teeth constitutes the slenderness ratio γ, and the value range of γ is 0.21~0.508. From γ<1, it can be seen that the inner arc thread teeth have a smaller C n and larger h n , the smaller C n This means that the average thickness of the internal arc thread teeth is smaller, coupled with the larger h n , making the inner arc thread teeth more slender, so the rigidity of the inner arc thread teeth is smaller. When the inner and outer arc thread teeth interact with each other, the inner arc thread teeth are more likely to bend and deform. When the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb the inertia force by bending and deforming, thereby reducing the bending deformation of the outer arc thread teeth, improving the ability of the outer arc thread to resist fatigue fracture, and improving the fatigue performance of the outer arc thread. Of course, too small C n and too large h n It also means that the internal arc thread teeth are too slender, which will cause the stiffness of the internal arc thread teeth to be too small, and thus cause the static load bearing capacity of the internal arc thread to drop significantly. After testing, it has been verified that only when γ is in the appropriate range of 0.21 to 0.508 can the internal arc thread be guaranteed to have sufficient static load bearing capacity, and at the same time the external arc thread has good fatigue performance.

[0009] Furthermore, the pitch of the internal arc thread is defined as P2, and the pitch of the external arc thread is defined as P1, then P2 = (1 to 1.0094) P1.

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

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

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

[0013] Furthermore, the inner tooth side straight segment and the outer tooth side straight segment are in contact with each other, and the tooth height of the external arc thread is defined as h w , the minor diameter is d1, the minor diameter of the internal arc thread is D1, then

[0014] Furthermore, the intersection of the inner tooth side straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc, and the radius of the outer tooth bottom arc is defined as R1, the minor diameter of the inner arc thread is D1, and the minor diameter of the outer arc thread is d1, then

[0015]

[0016] To achieve the above purpose, the internal arc thread in the present invention adopts the following technical solutions:

[0017] An internal arc thread, the thread profile of which includes an inner tooth bottom 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, and the width of the inner tooth top straight line segment is defined as C n , the tooth height of the internal arc thread is h n , then the slenderness ratio of the internal arc thread tooth is The value range of γ is 0.21~0.508.

[0018] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further limits the width C of the inner tooth top straight line segment. n The tooth height h of the internal arc thread n The ratio of the inner arc thread teeth constitutes the slenderness ratio γ, and the value range of γ is 0.21~0.508. From γ<1, it can be seen that the inner arc thread teeth have a smaller C n and larger h n , the smaller C n This means that the average thickness of the internal arc thread teeth is smaller, coupled with the larger h n, making the inner arc thread teeth more slender, so the rigidity of the inner arc thread teeth is smaller. When the inner and outer arc thread teeth interact with each other, the inner arc thread teeth are more likely to bend and deform. When the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb the inertia force by bending and deforming, thereby reducing the bending deformation of the outer arc thread teeth, improving the ability of the outer arc thread to resist fatigue fracture, and improving the fatigue performance of the outer arc thread. Of course, too small C n and too large h n It also means that the internal arc thread teeth are too slender, which will cause the stiffness of the internal arc thread teeth to be too small, and thus cause the static load bearing capacity of the internal arc thread to drop significantly. After testing, it has been verified that only when γ is in the appropriate range of 0.21 to 0.508 can the internal arc thread be guaranteed to have sufficient static load bearing capacity, and at the same time the external arc thread has good fatigue performance.

[0019] Furthermore, the pitch of the internal arc thread is defined as P2, then P2 = (1-1.0094) P1, where P1 is the pitch of the external arc thread adapted to the internal arc thread.

[0020] Furthermore, P2=(1.0015~1.0079)P1.

[0021] Furthermore, the pitch of the internal arc thread is defined as P2, then h n =(0.28~0.54)P2.

[0022] Furthermore, the pitch of the internal arc thread is defined as P2, then 0.1P2≤C n ≤0.175P2.

[0023] To achieve the above purpose, the nut in the present invention adopts the following technical solutions:

[0024] A nut is provided with an internal arc thread. The tooth profile of the internal arc thread includes an inner tooth bottom 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 width of the inner tooth top straight line segment is defined as C. n , the tooth height of the internal arc thread is h n , then the slenderness ratio of the internal arc thread tooth is The value range of γ is 0.21~0.508.

[0025] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further limits the width C of the inner tooth top straight line segment. n The tooth height h of the internal arc thread n The ratio of the inner arc thread teeth constitutes the slenderness ratio γ, and the value range of γ is 0.21~0.508. From γ<1, it can be seen that the inner arc thread teeth have a smaller C n and larger hn , the smaller C n This means that the average thickness of the internal arc thread teeth is smaller, coupled with the larger h n , making the inner arc thread teeth more slender, so the rigidity of the inner arc thread teeth is smaller. When the inner and outer arc thread teeth interact with each other, the inner arc thread teeth are more likely to bend and deform. When the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb the inertia force by bending and deforming, thereby reducing the bending deformation of the outer arc thread teeth, improving the ability of the outer arc thread to resist fatigue fracture, and improving the fatigue performance of the outer arc thread. Of course, too small C n and too large h n It also means that the internal arc thread teeth are too slender, which will cause the stiffness of the internal arc thread teeth to be too small, and thus cause the static load bearing capacity of the internal arc thread to drop significantly. After testing, it has been verified that only when γ is in the appropriate range of 0.21 to 0.508 can the internal arc thread be guaranteed to have sufficient static load bearing capacity, and at the same time the external arc thread has good fatigue performance.

[0026] Furthermore, the pitch of the internal arc thread is defined as P2, then P2 = (1-1.0094) P1, where P1 is the pitch of the external arc thread adapted to the internal arc thread.

[0027] Furthermore, P2=(1.0015~1.0079)P1.

[0028] Furthermore, the pitch of the internal arc thread is defined as P2, then h n =(0.28~0.54)P2.

[0029] Furthermore, the pitch of the internal arc thread is defined as P2, then 0.1P2≤C n ≤0.175P2. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the tooth profile of the external arc thread in the first embodiment of the arc thread connection pair of the present invention;

[0031] Figure 2 Schematic diagram of the tooth profile of the internal arc thread in the first embodiment of the arc thread connection pair of the present invention;

[0032] Figure 3 Schematic diagram of the tooth profile matching of the internal arc thread and the external arc thread in the first embodiment of the arc thread connection pair of the present invention;

[0033] Figure 4 Schematic diagram of the calibration position of the external arc thread in the first embodiment of the arc thread connection pair of the present invention;

[0034] Figure 5Graph showing the average stress variation over time at a calibrated position of the outer arc threads of thread pair 1, thread pair 2, thread pair 3, thread pair 4, thread pair 5 and comparative thread pair 1 under alternating load in the first embodiment of the arc thread connection pair of the present invention;

[0035] Figure 6 The load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under alternating loads when the slenderness ratio γ is 0.577 in the first embodiment of the circular arc thread connection pair of the present invention;

[0036] Figure 7 The load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under alternating loads when the slenderness ratio γ is 0.341 in the first embodiment of the circular arc thread connection pair of the present invention;

[0037] Figure 8 The load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different slenderness ratios and different pitches in the first embodiment of the arc thread connection pair of the present invention under the action of alternating loads;

[0038] Figure 9 Schematic diagram of the tooth profile matching of the internal arc thread and the external arc thread in the second embodiment of the arc thread connection pair of the present invention;

[0039] Figure 10 Graph showing the average stress variation over time at a calibrated position of the outer arc threads of thread pairs 7, 8, 9, 10, and 11 in Embodiment 2 of the circular arc thread connection pair of the present invention and comparison thread pair 3 under alternating loads;

[0040] Figure 11 The load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under alternating loads when the slenderness ratio γ is 0.577 in the second embodiment of the circular arc thread connection pair of the present invention;

[0041] Figure 12 The load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under alternating loads when the slenderness ratio γ is 0.341 in the second embodiment of the arc thread connection pair of the present invention;

[0042] Figure 13 It is the load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different slenderness ratios and different pitches in the second embodiment of the arc thread connection pair of the present invention under the action of alternating loads.

[0043] In the figure: 1, external arc thread; 11, external thread top; 12, external tooth side straight segment; 13, external tooth bottom arc; 2, internal arc thread; 21, internal tooth bottom arc; 22, internal tooth side straight segment; 23, internal tooth top straight segment. DETAILED DESCRIPTION

[0044] In view of the technical problems existing in the prior art, the basic concept of the present invention is to limit the width C of the inner tooth top straight line segment. n The tooth height h of the internal arc thread n When the ratio γ is within an appropriate range, the arc thread teeth are relatively slender, the stiffness of the inner arc thread teeth is relatively small, and when the inner and outer arc thread teeth interact with each other, the inner arc thread teeth are more likely to bend and deform. When the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb the inertia force through bending deformation, thereby reducing the bending deformation of the outer arc thread teeth, improving the ability of the outer arc thread to resist fatigue fracture, and improving the fatigue performance of the outer arc thread.

[0045] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0046] Implementation method 1 of the arc thread connection pair in the present invention:

[0047] like Figure 4 As shown, the arc thread connection pair includes an outer arc thread 1 and an inner arc thread 2 that cooperate with each other. The outer arc thread 1 is set on the bolt or the stud, and the inner arc thread 2 is set on the nut. Therefore, the arc thread connection pair can be an ordinary bolt connection pair including a bolt + nut, a high-strength bolt connection pair including a bolt + nut + washer, or a stud pair including a stud + nuts at both ends.

[0048] like Figure 1 As shown, the thread profile of the external arc thread 1 includes an external thread crest 11, an external flank straight segment 12, an external root arc 13, and an external flank straight segment 12, which are connected in sequence. In this embodiment, the external thread crest 11 is arc-shaped, and the external flank straight segment 12 is tangent to the external thread crest 11 and the external root arc 13, respectively. In other embodiments, the external thread crest 11 may also extend in a straight line, in which case the external flank straight segment 12 is tangent only to the external root arc 13.

[0049] The two adjacent outer tooth side straight sections 12 are symmetrical, and the angle α between the two adjacent outer tooth side straight sections 12 is the tooth profile angle of the external arc thread. The range of α is: 40° to 80°, and is generally preferably 60°. In addition, the pitch of the external arc thread is P1, the minor diameter is d1, the major diameter is d, the radius of the external tooth bottom arc 13 is R1, the radius of the external thread crest 11 is R2, and the tooth height of the external arc thread is h wIn fact, the structure of the external arc thread is the existing technology, and the present invention does not improve the external arc thread.

[0050] like Figure 2 As shown, the tooth profile of the internal arc thread 2 includes an inner tooth bottom arc 21, an inner tooth side straight segment 22, an inner tooth top straight segment 23 and an inner tooth side straight segment 22 connected in sequence, wherein the inner tooth side straight segment 22 is tangent to the inner tooth bottom arc 21. Two adjacent inner tooth side straight segments 22 are symmetrical, and the angle β between the two adjacent inner tooth side straight segments 22 is the tooth profile angle of the internal arc thread. In addition, the pitch of the internal arc thread is P2, the minor diameter is D1, the major diameter is D, and the width of the inner tooth top straight segment 23 is C n The radius of the inner tooth bottom arc 21 is r, and the tooth height of the inner arc thread is h n .

[0051] like Figure 3 As shown, in this embodiment, β=α, and the inner tooth side straight section 22 is in contact with the outer tooth side straight section 12. In order to ensure that there is a certain contact area between the inner and outer arc threads, there is a certain overlap rate between the inner and outer arc threads to avoid the inner and outer arc threads being stripped due to too small overlap rate, in this embodiment, it is limited That is, the distance between the inner tooth top straight section 23 and the outer arc thread tooth bottom cannot exceed half of the outer arc thread tooth height. Of course, in other embodiments, It may also be less than 0.49, 0.48, 0.47, 0.51, 0.52 or 0.53.

[0052] In the present invention, the width C of the inner tooth top straight line segment is defined as n The tooth height h of the internal arc thread n The ratio is the slenderness ratio γ of the inner arc thread tooth, that is, The value range of γ is 0.21~0.508. From this value range, it can be seen that γ<1 and the internal arc thread has a smaller C n and larger h n , the smaller C n This means that the average thickness of the internal arc thread teeth is smaller, coupled with the larger h n , making the inner arc thread teeth more slender, so the rigidity of the inner arc thread teeth is smaller. When the inner and outer arc thread teeth interact with each other, the inner arc thread teeth are more likely to bend and deform. When the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb the inertia force by bending and deformation, thereby reducing the bending deformation of the outer arc thread teeth, improving the ability of the outer arc thread to resist fatigue fracture, and improving the fatigue performance of the outer arc thread.

[0053] Of course, too small C n and too large h nIt also means that the internal arc thread teeth are too slender, which will cause the stiffness of the internal arc thread teeth to be too small, and thus cause the static load bearing capacity of the internal arc thread to drop significantly. After testing, it has been verified that only when γ is in the appropriate range of 0.21 to 0.508 can the internal arc thread be guaranteed to have sufficient static load bearing capacity, and at the same time the external arc thread has good fatigue performance.

[0054] Furthermore, under the premise of ensuring that the value range of γ is 0.21~0.508, this embodiment defines h n =(0.28~0.54)P2,0.1P2≤C n ≤0.175P2, for determining C in practical engineering applications n and h n Of course, in other embodiments, as long as the value 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 above range.

[0055] In addition, as Example 1, the pitches of the internal arc thread and the external arc thread in this embodiment are equal, that is, P1 = P2. To verify the superiority of the arc thread connection pair in this embodiment, six thread pair structures are given below, with specific thread parameters as shown in Table 1. Among them, comparative thread pair 1 is an existing arc thread connection pair, and its internal and external arc thread profiles are both existing technologies, and the slenderness ratio γ of the internal 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 is the different slenderness ratios γ of the internal arc threads. The slenderness ratios γ of the internal arc threads of thread pair 1, thread pair 2, thread pair 3, and thread pair 4 are between 0.21 and 0.508, and the slenderness ratio γ of the internal arc thread of thread pair 5 is less than 0.21.

[0056] Table 1 Specific thread parameters of Example 1 in Implementation Method 1

[0057]

[0058]

[0059] Based on the above parameters, tensile strength tests were conducted on bolts and nuts. This involved applying a fixed constraint to the nut and loading the bolt with increasing tensile force. The tensile strengths of the bolts corresponding to different thread pairs were measured, as shown in Table 2. Three samples were used to test bolts with the same thread parameters.

[0060] Table 2 Tensile strength of bolts corresponding to each thread pair of Example 1 in Implementation Method 1

[0061]

[0062] From the results in Table 2, it can be seen that the overall tensile strength of the bolts corresponding to thread pair 1, thread pair 1, thread pair 2, thread pair 3, and thread pair 4 are at the same level. The slenderness ratio of the inner arc thread of the nut corresponding to thread pair 5 is too large. When loaded, the inner arc thread teeth produce large bending deformation. When the loading force is far less than the loading force of other bolts, the bolt and nut will be disengaged, indicating that the deformation of the inner arc thread teeth is too large and the static load bearing capacity is extremely poor.

[0063] At the same time, according to the thread parameters in Table 1, the present invention also uses general finite element analysis software to perform dynamic analysis on the internal and external arc threads, that is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is applied to the bolt or stud. Under the same alternating load, the external arc threads in the six thread pairs are obtained at the calibration position (calibration position is Figure 4 The red position in the figure is the first thread position of the external arc thread, which is usually the position where the stress is most concentrated. The average stress at this position changes with time, as shown in the figure. Figure 5 shown.

[0064] from Figure 5 It can be seen from the figure that at each loading moment, the average stress of the outer arc thread in thread pair 1 to thread pair 5 at the calibration position is less than the average stress of the outer arc thread in thread pair 1 at the calibration position, and the average stress of the outer arc thread in thread pair 5 at the calibration position is always the smallest, and increases in thread pair 4, thread pair 3, thread pair 2, and thread pair 1 respectively, indicating that as the slenderness ratio γ gradually decreases, the average stress of the outer arc thread at the calibration position gradually decreases, which confirms that the slenderer the inner arc thread teeth, the smaller the stiffness of the inner arc thread teeth, and the easier the inner arc thread teeth are to bend and deform. Therefore, when the inner and outer arc threads are subjected to alternating loads, the inner arc thread teeth can absorb more inertia force through bending deformation, reduce the bending deformation of the outer arc thread teeth, and improve the fatigue performance of the outer arc thread.

[0065] Of course, through the above tensile strength test, we can know that the bolts and nuts in thread pair 5 are disengaged, which is impossible to use in actual engineering. Therefore, according to the results in Table 2, under the premise that the overall tensile strength of the bolts corresponding to thread pair 1, thread pair 1, thread pair 2, thread pair 3, and thread pair 4 are at the same level, combined with Figure 5 It can be seen that thread pair 4 is the best, that is, under the premise of ensuring that the internal arc thread has sufficient static load bearing capacity, the smaller the slenderness ratio γ of the internal arc thread is, the more significant the effect of improving the fatigue performance of the external arc thread is.

[0066] In addition, in order to compare the influence of unequal pitch on the fatigue performance of external arc thread, Example 2 is also provided in this embodiment. In Example 2, the pitch P2 of the internal arc thread is greater than the pitch P1 of the external arc thread, specifically P2 = (1 ~ 1.0094) P1, and preferably P2 = (1.0015 ~ 1.0079) P1.

[0067] According to known research in the prior art, when internal and external threads of equal pitch are under load, the external thread is subjected to tensile elongation, and the internal thread is subjected to compressive compression. 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 press the connected parts) has a large elongation, and the external thread away from the support surface has a small elongation. This causes the axial load of the threaded connection pair to be mainly borne by the first three circles (i.e., the first three buckles) of threads close to the support surface, and the subsequent threads are almost not subjected to stress, resulting in significant stress concentration in the first three circles of threads, and the first circle of threads carries the largest load, followed by the second circle, and the third circle is even smaller.

[0068] Based on this, in this embodiment, the pitch P2 of the internal arc thread is designed to be greater than the pitch P1 of the external arc thread, so that the internal and external arc threads can preferentially contact each other away from the connected parts (i.e., away from the support surface), and then the internal and external arc threads can be made to contact one by one in the process of increasing the load to the rated preload, which can effectively improve the load uniformity of each circle of thread teeth under the action of the rated preload. Therefore, when the internal and external arc threads are subjected to alternating loads with an average load of the rated preload, the engagement length of the internal and external arc threads changes with the change of the load, thereby preventing obvious load concentration in a certain circle of threads.

[0069] At the same time, for internal arc threads with a slenderness ratio γ in the range of 0.21 to 0.508, the internal arc thread teeth have low stiffness and are prone to bending and deformation. If the internal and external arc threads with equal pitch are still used, the first circle of threads will bear the greatest load, and the internal arc thread teeth will have insufficient stiffness, which will easily lead to broken teeth. After the first circle of internal arc thread teeth breaks, the second circle of threads will begin to bear the load and face the same problem, eventually causing the bolt and nut to completely disengage. However, after designing the pitch P2 of the internal arc thread to be greater than the pitch P1 of the external arc thread, the load uniformity of each circle of threads is improved. That is, when the internal and external arc threads are subjected to alternating loads, each circle of threads is subjected to force simultaneously, and the load is no longer concentrated on the first three circles of threads. Therefore, even if the internal arc thread teeth have low stiffness and are prone to bending and deformation, the normal use of the bolt and nut can be guaranteed.

[0070] Of course, the pitch P2 of the internal arc thread cannot be too large and must be within an appropriate range. Otherwise, under the premise that the internal and external arc threads preferentially contact each other at a point away from the connected part (i.e., away from the support surface), as the load gradually increases, the subsequent threads cannot achieve effective one-to-one contact, but instead cause the threads away from the connected part (i.e., away from the support surface) to be subjected to excessive force, which is the same effect as the first circle of medium-pitch threads in the prior art that bear too much load. This is not the desired result of the present invention.

[0071] Experimental verification shows that when P2 = (1 ~ 1.0094) P1, it can not only effectively improve the load ratio of each circle of thread teeth and enhance the fatigue performance of the external arc thread, but also solve the problem of insufficient load capacity caused by the internal arc thread teeth being too slender.

[0072] To verify the superiority of this embodiment, a comparative test was conducted as shown in Table 3. This embodiment retains comparative thread pair 1, thread pair 1, and thread pair 2, 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 internal arc thread. Since P1 = 6.35, 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 internal arc thread of comparative thread pair 1 is exactly the end value and is not within the preferred range, while the pitch of the internal arc thread of comparative thread pair 2 is within the preferred range.

[0073] Table 3 Specific thread parameters of Example 2 in Implementation Method 1

[0074]

[0075]

[0076] Secondly, the difference between thread pair 2 and thread pair 6 is that the pitch of the inner and outer arc threads in thread pair 2 is equal, while the pitch of the inner arc threads in thread pair 6 is within the preferred range. Furthermore, the slenderness ratio γ of the inner arc threads in both thread pairs 2 and 6 is within the range of 0.21 to 0.508.

[0077] One of the similarities between the comparative thread pair 2 and the thread pair 6 is that the pitch of the internal arc thread is within the preferred range. The difference is that the slenderness ratio γ of the internal arc thread in the thread pair 6 is in the range of 0.21 to 0.508, while the slenderness ratio γ of the internal arc thread in the comparative thread pair 2 is greater than 0.508.

[0078] The pitch of the internal arc thread of the thread pair 1 is also an extreme value and is also out of the preferred range, but the slenderness ratio γ of the internal arc thread is 0.508.

[0079] According to the above parameters, fatigue tests were carried out on bolts and nuts. Table 4 shows the number of cycles of comparison thread pair 1, comparison thread pair 2, thread pair 2, and thread pair 6 under the same load on the same fatigue test equipment.

[0080] Table 4 Fatigue cycle number

[0081] Sample Thread pair 1 Thread pair 2 Thread pair 6 Compare thread pair 1 Compare thread pair 2 Sample 1 614,000 times 1.295 million times Over 5 million times 253,000 times 1.741 million times Sample 2 565,000 times 1.424 million times Over 5 million times 421,000 times 1.487 million times Sample 3 491,000 times 1.374 million times 4.626 million times 331,000 times 2.069 million times

[0082] As can be seen from Table 4, comparative thread pair 1 is an existing circular arc thread structure with the lowest fatigue life. Comparative thread pair 2 is based on the existing circular arc thread, but the pitch P2 of the internal circular arc thread is within the preferred range, and the fatigue life of the thread pair is improved. The slenderness ratio γ of the internal circular arc thread in thread pair 2 is between 0.21 and 0.508, and the number of cycles of the thread pair is significantly higher than that of the existing circular arc thread profile. The pitch P2 of the internal circular arc thread in thread pair 6 is within the preferred range, and the slenderness ratio γ of the internal circular arc thread is between 0.21 and 0.508. The number of fatigue cycles of the thread pair is the highest, which is consistent with the previous theoretical analysis results.

[0083] It should be noted that Table 4 also shows that for Comparative Thread Pairs 1, 1, and 2, which have equal pitches of internal arc threads (P2 of 6.35), the fatigue life of the connection pairs increases as the slenderness ratio γ of the internal arc threads decreases. Comparative Thread Pair 1, with a slenderness ratio of 0.577, has the worst fatigue life compared to the other connection pairs, so it was discarded. The upper limit of the slenderness ratio γ is thus determined to be 0.508. Of course, for Comparative Thread Pairs 2 and 6, which have equal pitches of internal arc threads (P2 of 6.38), although the slenderness ratio γ of Comparative Thread Pair 2 is 0.577, exceeding the optimal range, the number of fatigue cycles is not low because the pitch P2 is within the preferred range.

[0084] Since the idea of this embodiment is to improve the load uniformity of each circle of the external arc thread by changing the pitch of the internal arc thread, while reducing the maximum load of the thread, the load ratio of each circle of the external arc thread used in combination with internal arc threads of different pitches under alternating loads is explored next under the condition of the same slenderness ratio γ.

[0085] First, the pitch of the external arc thread is defined as P1 = 6.35mm and the minor diameter d1 = 30.6mm. The slenderness ratio γ of the internal arc thread is 0.577 and the minor diameter D1 is 32.2mm. The pitch P2 of several internal arc threads are 6.35mm, 6.36mm, 6.38mm, 6.40mm, 6.41mm and 6.42mm respectively. The dynamic analysis of the internal and external arc threads is carried out using general finite element analysis software. That is, 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 6 The figure shows the load ratio of each thread circle of the external arc thread used in conjunction with the internal arc thread of different pitches at the 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 circle of the external arc thread is not only very poor, but the load ratio of the seventh circle is even higher than the maximum load ratio in the prior art (P2=6.35mm). At the same time, 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 value of P2 is selected as 6.41mm, corresponding to the range of P2 defined above is (1~1.0094)P1.

[0086] 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 circle is better than the load uniformity of the end value (P2 is 6.35mm and 6.41mm), corresponding to the preferred range of P2 defined above is (1.0015~1.0079)P1.

[0087] Secondly, this embodiment also gives the load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under the action of alternating loads when the slenderness ratio γ is 0.341, as shown in FIG. Figure 7 As shown in the figure, when P2=6.42mm, that is, when P2>6.41mm, the load uniformity of each circle of the external arc thread is not only very poor, but also the load ratio of the seventh circle is higher than the maximum load ratio of the prior art (P2=6.35mm). At the same time, considering that the maximum load ratio when P2=6.41mm does not exceed the maximum load ratio of the prior art (P2=6.35mm), the upper limit of P2 is selected as 6.41mm, corresponding to the range of P2 defined above as (1~1.0094)P1. At the same time, from Figure 7 It can also be seen that when P2 is 6.36mm, 6.38mm, and 6.40mm, the load uniformity of each circle is better than the load uniformity of the end value (P2 is 6.35mm and 6.41mm), corresponding to the preferred range of P2 defined above is (1.0015~1.0079)P1.

[0088] Therefore, combined Figure 6 and Figure 7 It can be seen that even if the slenderness ratio γ is different, the change law of the load ratio of each circle of the external arc thread used in combination with the internal arc thread with different pitches under the action of alternating load is consistent. Under different values of the slenderness ratio γ, the value range and preferred range of the pitch P2 of the internal arc thread are consistent.

[0089] Further, if Figure 8 The figure shows the load ratio of each circle of the external arc thread used in combination with the internal arc thread with different slenderness ratios and different pitches under the action of alternating loads. It can be seen from the figure that when the slenderness ratio γ of the internal arc thread is 0.577 and is not in the range of 0.21 to 0.508, the load uniformity of each circle of the external arc thread corresponding to the internal arc thread with a larger pitch P2 (P2 = 6.38 mm, within the preferred range) is better, which proves that even if the slenderness ratio γ is not preferred, only increasing the pitch of the internal arc thread can improve the load uniformity of each circle of the external arc thread.

[0090] When the pitch P2 of the internal arc thread is 6.35 mm, the load uniformity of each circle of the external arc thread corresponding to the internal arc thread with a smaller slenderness ratio γ (γ = 0.341, in the range of 0.21 to 0.508) is better, which proves that when the pitch of the internal and external arc threads is equal, only reducing the slenderness ratio γ of the internal arc thread can also improve the load uniformity of each circle of the external arc thread.

[0091] When the slenderness ratio γ of the internal arc thread is 0.341 and is within the range of 0.21 to 0.508, the load uniformity of each circle of the external arc thread corresponding to the internal arc thread with a larger pitch P2 (P2 = 6.38 mm, within the preferred range) is better, and is the best among several threads. This proves that after the superposition of the slenderness ratio γ and pitch P2, the load uniformity of each circle of the external arc thread is improved the most.

[0092] Implementation method 2 of the arc thread connection pair in the present invention:

[0093] The difference between the second embodiment and the first embodiment lies in the contact position of the inner arc thread and the outer arc thread. In the second embodiment, Figure 9 As shown, line segment AB represents the outer flank straight segment 12, point B represents the tangent point between the outer flank straight segment 12 and the outer root arc 13, and the intersection of the inner flank straight segment 22 and the inner crest straight segment 23 contacts the outer root arc 13 at point C. Compared to embodiment 1, the contact point between the inner and outer arc threads in embodiment 2 is closer to the outer arc thread root. B' in the figure represents the tangent point between the outer root arc 13 and the other outer flank straight segment. The inner crest straight segment 23 is located on the side of BB' closer to the outer arc thread axis.

[0094] In order to ensure that the inner and outer arc threads can contact normally in structure, and the contact point is on the outer tooth bottom arc 13, the width C of the inner tooth top straight line segment 23 must be ensured. n ≤CC', where C is the contact point of the inner and outer arc threads, and C' is the intersection of the extension line of the inner tooth top straight line segment 23 and the outer tooth bottom arc 13. Otherwise, if C n >CC', the inner tooth top straight section 23 cannot be accommodated between CC', and the inner and outer arc threads cannot be matched.

[0095] In addition, point O in the figure is the center of the outer tooth bottom arc 13, OE is perpendicular to the axis of the outer arc thread, point E is on the outer tooth bottom arc 13, OE is perpendicular to CC', and OE and CC' intersect at point F, OC = OE = R1. According to the geometric relationship, we can know that: so

[0096] In order to verify the superiority of the arc thread connection pair in Implementation Method 2, six thread pair structures are given below. The specific thread parameters are shown in Table 5. The difference compared with Example 1 (Table 1) in Implementation Method 1 is that the minor diameter D1 of the internal arc thread is different. The minor diameter D1 of the internal arc thread in Implementation Method 2 is smaller, so that the intersection of the inner tooth side straight line segment and the inner tooth top straight line segment can contact the outer tooth bottom arc.

[0097] Table 5 Specific thread parameters in embodiment 2

[0098]

[0099]

[0100] Based on the above parameters, tensile strength tests were conducted on the bolts and nuts. That is, a fixed constraint was applied to the nut and a continuously increasing tensile force was applied to the bolt. The tensile strengths of the bolts corresponding to different thread pairs were measured and shown in Table 6.

[0101] Table 6 Tensile strength of bolts corresponding to each thread pair in the second embodiment

[0102]

[0103] In the second embodiment, since the intersection of the inner tooth side straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc, the overlap rate between the inner and outer thread teeth becomes larger, and the load-bearing performance of the thread teeth is increased, so there is no disengagement between the bolt and the nut, and even the thread pair 11 with the smallest slenderness ratio γ does not exhibit disengagement.

[0104] At the same time, according to the thread parameters in Table 5, the general finite element analysis software is used to perform dynamic analysis on the internal and external arc threads. That is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is applied to the bolt or stud. Under the same alternating load, the average stress variation curve of the external arc thread in the six thread pairs at the calibration position (calibration position is the same as above) is obtained. Figure 10 shown.

[0105] from Figure 10 As can be seen in the figure, at each loading moment, the average stress of the outer arc threads in thread pairs 7 to 11 at the calibration position is lower than the average stress of the outer arc threads in comparison thread pair 3 at the calibration position, and the average stress of the outer arc threads in thread pair 11 at the calibration position is always the smallest. As the slenderness ratio γ gradually decreases, the average stress of the outer arc threads at the calibration position gradually decreases, confirming that the slenderer the inner arc threads, the lower the stiffness of the inner arc threads and the more prone they are to bending deformation. Therefore, when the inner and outer arc threads are subjected to alternating loads, the inner arc threads can absorb more inertial forces through bending deformation, reducing the bending deformation of the outer arc threads and improving the fatigue performance of the outer arc threads.

[0106] Of course, the above tensile strength test shows that, under the premise that the overall tensile strength of the bolts corresponding to thread pairs 7 to 11 and comparison thread pair 3 are at the same level, thread pair 11 is the best. In other words, under the premise of ensuring that the internal arc thread has sufficient static load bearing capacity, the smaller the slenderness ratio γ of the internal arc thread is, the more significant the effect of improving the fatigue performance of the external arc thread.

[0107] Furthermore, this embodiment also explores the load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under the action of alternating loads when the slenderness ratio γ is the same.

[0108] First, when the slenderness ratio γ of the internal arc thread is 0.577 and the minor diameter D1 is 31.5mm, the pitch P1 of the external arc thread is 6.35mm and the minor diameter d1 is 30.6mm, the pitch P2 of several internal arc threads are 6.35mm, 6.36mm, 6.38mm, 6.40mm, 6.41mm and 6.42mm respectively. The general finite element analysis software is used to perform dynamic analysis on the internal and external arc threads, that is, a fixed constraint is applied to the nut, and an alternating load that varies with time is applied to the bolt or stud. Under the same alternating load, Figure 11The figure shows the load ratio of each thread circle of the external arc thread used in conjunction with the internal arc thread of different pitches at the 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 circle of the external arc thread is not only very poor, but the load ratio of the seventh circle is even higher than the maximum load ratio in the prior art (P2=6.35mm). At the same time, 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 value of P2 is selected as 6.41mm, corresponding to the range of P2 defined above is (1~1.0094)P1.

[0109] 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 circle is better than the load uniformity of the end value (P2 is 6.35mm and 6.41mm), corresponding to the preferred range of P2 defined above is (1.0015~1.0079)P1.

[0110] This embodiment also provides the load ratio of each thread circle of the external arc thread used in conjunction with internal arc threads of different pitches under the action of alternating loads when the slenderness ratio γ is 0.341, as shown in FIG. Figure 12 As shown in the figure, when P2=6.42mm, that is, when P2>6.41mm, the load uniformity of each circle of the external arc thread is not only very poor, but also the load ratio of the seventh circle is higher than the maximum load ratio of the prior art (P2=6.35mm). At the same time, considering that the maximum load ratio when P2=6.41mm does not exceed the maximum load ratio of the prior art (P2=6.35mm), the upper limit of P2 is selected as 6.41mm, corresponding to the range of P2 defined above as (1~1.0094)P1. At the same time, from Figure 12 It can also be seen that when P2 is 6.36mm, 6.38mm, and 6.40mm, the load uniformity of each circle is better than the load uniformity of the end value (P2 is 6.35mm and 6.41mm), corresponding to the preferred range of P2 defined above is (1.0015~1.0079)P1.

[0111] Therefore, combined Figure 11 and Figure 12 It can be seen that even if the slenderness ratio γ is different, the change law of the load ratio of each circle of the external arc thread used in combination with the internal arc thread with different pitches under the action of alternating load is consistent. Under different values of the slenderness ratio γ, the value range and preferred range of the pitch P2 of the internal arc thread are consistent.

[0112] Furthermore, if Figure 13The figure shows the load ratio of each circle of the external arc thread used in combination with the internal arc thread with different slenderness ratios and different pitches under the action of alternating loads. It can be seen from the figure that when the slenderness ratio γ of the internal arc thread is 0.577 and is not in the range of 0.21 to 0.508, the load uniformity of each circle of the external arc thread corresponding to the internal arc thread with a larger pitch P2 (P2 = 6.38 mm, within the preferred range) is better, which proves that even if the slenderness ratio γ is not preferred, only increasing the pitch of the internal arc thread can improve the load uniformity of each circle of the external arc thread.

[0113] When the pitch P2 of the internal arc thread is 6.35 mm, the load uniformity of each circle of the external arc thread corresponding to the internal arc thread with a smaller slenderness ratio γ (γ = 0.341, in the range of 0.21 to 0.508) is better, which proves that when the pitch of the internal and external arc threads is equal, only reducing the slenderness ratio γ of the internal arc thread can also improve the load uniformity of each circle of the external arc thread.

[0114] When the slenderness ratio γ of the internal arc thread is 0.341 and is within the range of 0.21 to 0.508, the load uniformity of each circle of the external arc thread corresponding to the internal arc thread with a larger pitch P2 (P2 = 6.38 mm, within the preferred range) is better, and is the best among several threads. This proves that after the superposition of the slenderness ratio γ and pitch P2, the load uniformity of each circle of the external arc thread is improved the most.

[0115] In other embodiments of the arc thread connection pair: different from the first and second embodiments, the tooth angles of the internal and external arc threads may also be unequal, for example, the tooth angle of the internal arc thread is smaller than the tooth angle of the external arc thread.

[0116] The embodiment of the internal arc thread in the present invention is as follows: the specific structure of the internal arc thread is the same as the internal arc thread in any embodiment of the above-mentioned arc thread connection pair, and will not be repeated here.

[0117] The embodiment of the nut in the present invention is as follows: an internal arc thread is provided on the nut, and the specific structure of the internal arc thread is the same as the internal arc thread in any embodiment of the above-mentioned arc thread connection pair, which will not be repeated here.

[0118] 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. A circular arc thread connection pair, comprising an internal arc thread and an external arc thread that cooperate with each other, wherein the tooth profile of the internal arc thread comprises an inner tooth bottom arc, an inner tooth side straight segment, an inner tooth top straight segment, and an inner tooth side straight segment connected in sequence, and the tooth profile of the external arc thread comprises an outer thread top, an outer tooth side straight segment, an outer tooth bottom arc, and an outer tooth side straight segment connected in sequence, wherein the definition The width of the inner tooth top straight line segment is C n , the tooth height of the internal arc thread is h n , then the slenderness ratio of the internal arc thread tooth is The value range of γ is 0.21~0.

508.

2. The arc thread connection pair according to claim 1, characterized in that: The pitch of the internal arc thread is P2, and the pitch of the external arc thread is P1, then P2 = (1 ~ 1.0094) P1.

3. The arc thread connection pair according to claim 2, characterized in that: P2=(1.0015~1.0079)P1.

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

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

6. The arc thread connection pair according to any one of claims 1 to 3, characterized in that: The straight line segment on the inner tooth side is in contact with the straight line segment on the outer tooth side, and the tooth height of the external arc thread is defined as h w , the minor diameter is d1, the minor diameter of the internal arc thread is D1, then 7. The arc thread connection pair according to any one of claims 1 to 3, characterized in that: The intersection of the inner tooth side straight line segment and the inner tooth top straight line segment contacts the outer tooth bottom arc. The radius of the outer tooth bottom arc is defined as R1, the minor diameter of the inner arc thread is D1, and the minor diameter of the outer arc thread is d1.

8. An internal arc thread, wherein the thread profile of the internal arc thread comprises an inner tooth bottom 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 width of the inner tooth top straight line segment is C n , the tooth height of the internal arc thread is h n , then the slenderness ratio of the internal arc thread tooth is The value range of γ is 0.21~0.

508.

9. The internal arc thread according to claim 8, characterized in that: The pitch of the internal arc thread is P2, then P2=(1~1.0094)P1, where P1 is the pitch of the external arc thread adapted to the internal arc thread.

10. The internal arc thread according to claim 9, characterized in that: P2=(1.0015~1.0079)P1.

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

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

13. A nut having an internal arc thread, characterized in that: The internal arc thread is the internal arc thread according to any one of claims 8 to 12.

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