Anti-loose threaded connection for resisting complex variable load

Abstract

The invention discloses an anti-loose threaded connection capable of resisting complex variable loads, which comprises a threaded connecting piece, the threaded connecting piece comprises a screw rod and an internal thread matched with an external thread of the screw rod, and the contact surfaces of the external thread and the internal thread are first cambered surfaces; the two first cambered surfaces are equal in curvature radius and identical in protruding direction, the first cambered surfaces extend to the crest from the bottom of a thread of the threaded connecting piece, the bevel angle of the thread is increased along with increase of transverse alternating load or decrease of axial alternating load, and the bevel angle of the thread is decreased along with decrease of the transverse alternating load or increase of the axial alternating load. Compared with the prior art, when the transverse load F of threaded connection is increased or reduced and the thrust at the threaded contact position is close to the frictional resistance, the action point and direction of the positive pressure N1 and N2 can be changed by changing the pressure distribution at the contact curve due to the fact that the thread bevel angle b of the radial contact line of the thread is variable, and the purpose of permanent looseness prevention is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of thread locking prevention, and more particularly to a locking prevention thread connection that can withstand complex variable loads. Background Art

[0002] Generally speaking, the lead angle of the thread is less than the equivalent friction angle of the screw pair, and the connecting thread can meet the self-locking condition. Therefore, when the axial and transverse static loads and the working temperature change little, the thread connection will not loosen automatically. However, under the action of axial and transverse impacts, vibrations or alternating loads, and the influence of temperature changes, the circumferential friction force between the screw pairs may decrease or disappear instantaneously. After this phenomenon occurs repeatedly, the connection will loosen. The loosening of the thread connection will lead to a decrease in the pre-tightening force of the connected parts, the failure of the mechanical connection, and serious accidents.

[0003] When the thread connection is under the action of axial and transverse impacts, vibrations or alternating loads, and the influence of temperature changes, the reason for loosening is as follows: Figure 1 As shown, under the action of the axial alternating load Q (Q0~Q’) and the transverse alternating load F (-F~F) on the screw rod, normal pressures N1, N2, reaction forces R1, R2, and frictional resistances F f1 , F f2 will be generated on the triangular thread surface. Among them, the normal pressure N1 and the reaction force R1 form an included angle γ1, and the normal pressure N2 and the reaction force R2 form γ2. When the transverse load F is small, γ1 and γ2 are less than the equivalent friction angle, and the screw thread of the screw rod will not move laterally relative to the nut thread; when the transverse load F increases to be greater than the sum of the horizontal components of the frictional resistances F f1 , F f2 , γ1 and γ2 will be greater than the equivalent friction angle, and the screw thread of the screw rod will move laterally relative to the nut thread; when the transverse load F is reversed, similarly, the screw thread of the screw rod will move laterally in the reverse direction relative to the nut thread.

[0004] Assume that one turn of the nut thread is unfolded into an inclined plane, and the screw rod is topologized as a slider on the inclined plane. As Figure 2 shown, when the slider (i.e., the screw thread of the screw rod) is under the action of the transverse load F, the slider slides along the transverse straight inclined plane, thereby driving the slider to generate an entrained motion longitudinally along the inclined plane (i.e., the circumferential rotation of the screw thread of the screw rod), and the nut thread rotates circumferentially and loosens relative to the screw thread of the screw rod; when the axial force of the screw rod changes, the transverse force increases, and the temperature changes, due to the Poisson's ratio and thermal expansion and contraction of the material, transverse deformation and displacement will occur at the contact between the screw thread of the screw rod and the nut thread. Similarly, the entrained nut thread rotates circumferentially and loosens relative to the screw thread of the screw rod. Thus, it can be seen that when the thread connection is under the action of axial and transverse impacts, vibrations or alternating loads, and the influence of temperature changes, the nut thread will inevitably rotate circumferentially and loosen relative to the screw thread of the screw rod.

[0005] As can be seen from the above analysis, the reasons for the loosening of the existing trapezoidal, triangular, and serrated thread connections are as follows: (1) The contact surface of the connecting thread is a straight helical surface. When viewed in the axial plane, it is an oblique straight line. The circumferential expansion of the nut thread is an oblique plane, and the screw can be topologically transformed into a slider. (2) When the axial force of the screw changes, the lateral force increases, and the temperature changes. Due to the Poisson's ratio and thermal expansion and contraction of the material, the lateral deformation and displacement occur along the oblique straight line at the contact between the screw thread and the nut thread, causing the nut thread to rotate circumferentially relative to the screw thread and loosen, which is equivalent to a slider moving laterally on an oblique plane and driving the slider to produce an associated longitudinal movement along the inclined plane. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] Based on this, the present invention proposes an anti-loosening thread connection against complex variable loads, aiming to solve the problem that the screw and nut in the prior art will reverse and loosen under external loads.

[0008] (2) Technical solutions

[0009] To overcome the above problems or at least partially solve the above problems, the present invention provides an anti-loosening thread connection against complex variable loads, including a threaded connector. The threaded connector includes a screw and an internal thread that mates with the external thread of the screw. The contact surfaces of the external thread and the internal thread are both first arc surfaces. The curvature radii of the two first arc surfaces are equal and the convex directions are the same. The first arc surface extends from the root to the crest of the thread of the threaded connector. The thread angle increases as the lateral alternating load increases or the axial alternating load decreases, and the thread angle decreases as the lateral alternating load decreases or the axial alternating load increases.

[0010] Preferably, by calculating the curvature radius tolerance and curvature position tolerance of the first arc surface, the thread angle increases as the lateral alternating load increases or the axial alternating load decreases, and the thread angle decreases as the lateral alternating load decreases or the axial alternating load increases.

[0011] Preferably, the curvature radius tolerance and curvature position tolerance of the first arc surface are optimized by finite element calculation.

[0012] Preferably, the specific steps for optimizing the curvature radius tolerance and curvature position tolerance of the first arc surface by finite element calculation are as follows: In the finite element calculation, the initial values of the curvature radius tolerance and curvature position tolerance of the first arc surface are both zero, and the step size is 0.2 micrometers. Then iterative calculations are performed to ensure that the thread angle increases as the lateral alternating load increases or the axial alternating load decreases, and the thread angle decreases as the lateral alternating load decreases or the axial alternating load increases.

[0013] Preferably, the thickness of the thread at the root is the same as that of the triangular thread at the root, and the thickness of the thread of the screw at the pitch diameter is the same as that of the internal thread.

[0014] Preferably, the non-contact surfaces of the external thread and the internal thread are both second arc surfaces, and the second arc surface and the first arc surface are respectively arranged on both sides of the thread.

[0015] Preferably, the non-contact surfaces of the external thread and the internal thread are both inclined surfaces, the inclined surface and the first arc surface are respectively arranged on both sides of the thread, the first arc surface is a concave surface, and the thickness of the thread at the root is the same as that of the triangular thread at the root.

[0016] Preferably, the non-contact surfaces of the external thread and the internal thread are both inclined surfaces, the inclined surface and the first arc surface are respectively arranged on both sides of the thread, the first arc surface is a concave surface, and the forming angle at the inclined surface is 0°-5°.

[0017] (III) Beneficial effects

[0018] The anti-loosening thread connection for resisting complex variable loads of the present invention has the following advantages:

[0019] In the present invention, when the lateral load F of the thread connection increases or decreases, causing the thrust at the thread contact to approach the frictional resistance, since the thread angle β of the thread radial contact line is variable, the normal pressures N1 and N2 can change the acting point and direction by changing the pressure distribution at the contact curve, that is, by increasing β1 and decreasing β2, to resist the increase of the normal pressures N1 and N2 or compensate for the decrease of the normal pressures N1 and N2, so that the thrust at the thread contact will never be greater than the frictional resistance F f1 、F f2 , γ1 and γ2 will never be greater than the equivalent friction angle, the external thread will never reverse and loosen circumferentially relative to the screw thread, and the thread connection will thus achieve permanent anti-loosening. Description of the drawings

[0020] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings. The drawings are schematic and should not be construed as imposing any limitation on the present invention. In the drawings:

[0021] Figure 1 is the force-displacement analysis diagram of the triangular thread connection in the prior art;

[0022] Figure 2 is the topological diagram of the force-displacement analysis of the triangular thread connection in the prior art;

[0023] Figure 3 is the finite element force-displacement analysis diagram of the trapezoidal (β = 15°) thread connection;

[0024] Figure 4It is a finite element force-displacement analysis diagram of trapezoidal (β = 30°) thread connection;

[0025] Figure 5 It is a finite element force-displacement analysis diagram of trapezoidal (β = 45°) thread connection;

[0026] Figure 6 It is a force-displacement analysis diagram of the same-direction curved surface anti-loosening thread connection of the present invention;

[0027] Figure 7 It is a schematic diagram of the anti-loosening principle of the same-direction curved surface anti-loosening thread connection of the present invention;

[0028] Figure 8 It is a schematic structural diagram of the reverse-curved surface anti-loosening thread connection of the present invention;

[0029] Figure 9 It is a schematic structural diagram of the single-sided curved surface anti-loosening thread connection of the present invention;

[0030] Figure 10 It is a schematic structural diagram of the single-sided curved surface serrated anti-loosening thread connection of the present invention.

[0031] Explanation of reference numerals:

[0032] 1. Screw rod, 11. External thread, 2. Internal thread, 21. First arc surface, 22. Second arc surface, 23. Inclined surface. Detailed implementation manners

[0033] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following will combine the accompanying drawings to make a detailed description of the specific implementation manners of the present invention. Many specific details are elaborated in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described here. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0034] According to the existing domestic and foreign thread connection anti-loosening theories, in order to improve the self-locking performance of thread connections, the circumferential equivalent friction coefficient f of thread connections should be increased υ , and f υ = f / cosβ (where f is the friction coefficient; β is the thread profile angle). It can be seen from the formula that increasing the thread profile angle β can improve the anti-loosening performance of thread connections; however, through finite element calculations on the relaxation of trapezoidal (β = 15°), triangular (β = 30°), and serrated (β = 45°) thread connections under axial and transverse impacts, vibrations, or alternating loads, the results are as Figure 3 , Figure 4 and Figure 5As shown, the analysis result is contrary to the existing anti-loosening theories of threaded connections at home and abroad. It is not that the larger the thread angle β, the better the self-locking property of the threaded connection; instead, the larger the thread angle β, the larger the loosening angle of the threaded connection, and the easier it is to loosen; the smaller the thread angle β, the smaller the loosening angle of the threaded connection, but the thickness of the thread root decreases, and the connection strength decreases.

[0035] From the above conclusion, it can be seen that ensuring that the threaded connection does not loosen under static load, and also ensuring that the threaded connection does not loosen under dynamic load, and ensuring that the strength of the thread root is not weakened are the difficult problems to be solved by the present invention.

[0036] Refer to the appendix Figure 6 , this embodiment provides an anti-loosening threaded connection against complex variable loads, including a threaded connector. The threaded connector includes a screw rod 1 and an internal thread 2 that mates with the external thread 11 of the screw rod 1. The surfaces where the external thread 11 and the internal thread 2 are in contact are both first arc surfaces 21. The curvature radii of the first arc surface 21 on the external thread 11 and the first arc surface 21 on the internal thread 2 are equal and the convex directions are the same. The first arc surface 21 of the screw rod 1 and the first arc surface 21 of the external thread 11 are fitted together. The first arc surface 21 extends from the root to the top of the thread of the threaded connector, that is, the first arc surface 21 of the screw rod 1 extends from the root to the top of its thread, and the first arc surface 21 of the external thread 11 extends from the root to the top of its thread. The thread angle increases as the transverse alternating load increases or the axial alternating load decreases, and the thread angle decreases as the transverse alternating load decreases or the axial alternating load increases. Since the thread contact is a curve, when the positive pressure contact point changes, the angle β (thread angle β) between the positive pressure and the axis also changes. Through this setting, the threaded connector automatically adjusts the size and direction of the thread angle β at the positive pressure thread contact under transverse and alternating loads, achieving permanent anti-loosening.

[0037] As another implementation manner of the present invention: By calculating the curvature radius tolerance and curvature position tolerance of the first arc surface 21, the thread angle increases as the transverse alternating load increases or the axial alternating load decreases, and the thread angle decreases as the transverse alternating load decreases or the axial alternating load increases.

[0038] As another implementation manner of the present invention: Through finite element optimization, calculate the curvature radius tolerance and curvature position tolerance of the first arc surface 21.

[0039] As another implementation manner of the present invention: Refer to the appendix Figure 6-7, the specific steps for finite element optimization calculation of the curvature radius tolerance and curvature position tolerance of the first arc surface 21 are as follows: In the finite element optimization calculation, the initial values of the curvature radius tolerance and curvature position tolerance of the first arc surface 21 are both zero, and the step size is 0.2 micrometers. Then iterative calculations are carried out. The purpose of the iterative calculations is to ensure that the thread helix angle β1 increases as the transverse alternating load F increases or the axial alternating load Q decreases, and the thread helix angle β2 decreases as the transverse alternating load F decreases or the axial alternating load Q increases. For example, through finite element optimization calculation, the curvature radius tolerance and curvature position tolerance of the M20 thread are obtained. When the curvature radius tolerance of the M20 thread is 5 - 20 micrometers and the curvature position tolerance is 5 - 25, under the action of transverse and alternating loads, the thread connection automatically adjusts the magnitude and direction of the thread helix angle β at the positive pressure thread contact, achieving permanent loosening prevention. Specifically, under the action of the axial alternating load Q and the transverse alternating load F, the screw 1 will generate a positive pressure N1, a reaction force R1, a frictional resistance F f1 and a thrust F t1 at the first position on the first arc surface 21, and generate a positive pressure N2, a reaction force R2, a frictional resistance F f2 and a thrust F t2 at the second position on the first arc surface 21; the first position and the second position are respectively located on both sides of the screw 1, and the first position is lower than the second position. Refer to the appendix Figure 7 , when the transverse alternating load F increases or decreases, causing the thrusts F t1 、F t2 at the thread contact to approach the frictional resistances F f1 、F f2 respectively, since the first arc surface 21 extends from the root to the crest of the thread, the thread helix angles β1 at the first position and β2 at the second position of the thread radial contact line are variable. The positive pressures N1 and N2 can change the acting point and direction of the positive pressure by changing the pressure distribution at the contact curve to resist the increase of the positive pressures N1 and N2 or compensate for the decrease of the positive pressures N1 and N2, resulting in the thrusts F t1 and F t2 being respectively less than the frictional resistances F f1 and F f2 , γ1 and γ2 will never be greater than the equivalent friction angle. When the transverse alternating load F reaches F max to the left, the acting point of the positive pressure N1 moves to the left, and the angle β1 (thread helix angle β1) between the positive pressure N1 and the axis reaches the maximum value β 1max ; the acting point of the positive pressure N2 moves to the left, and the angle β2 (thread helix angle β2) between the positive pressure N2 and the axis reaches the maximum value β 2min , the minimum angle β min (the limit value is 0°) between the curve normal and the axis and the maximum angle β max(90°), respectively, the points where the distribution pressure is zero at both ends, that is, the screw thread angle β at both ends of the curve is as long as β min ~β max If the value is within the range, the external thread 11 of the threaded connection will never reverse and loosen relative to the circumferential direction of the screw 1, and the threaded connection will be permanently locked. Among them, the value range of the axial alternating load Q is: Q min ~Q max , the range of the transverse alternating load F is: -F min ~F max .

[0040] One embodiment of the threaded connector: Figure 6 The external thread 11 of the threaded connector is arranged on the nut, and the thickness of the thread at the root of the thread is the same as the thickness of the triangular thread at the root of the thread. This arrangement ensures that the thread strength is not weakened, and can effectively prevent the screw thread and the nut thread from lateral displacement at the contact point, solving the problem that the thread connection will inevitably produce circumferential reversal and loosening under the action of axial and lateral impact, vibration or alternating load. The thread thickness of the screw 1 at the mid-diameter is the same as the thread thickness of the internal thread 2. This arrangement ensures that the thread strength of the screw 1 and the nut is the same.

[0041] As another embodiment of the present invention: the non-contacting surfaces of the external thread 11 and the internal thread 2 are both second arc surfaces 22, and the second arc surface 22 and the first arc surface 21 are respectively arranged on both sides of the thread. Figure 6 The threaded connection is a same-direction curved anti-loosening threaded connection, wherein the first arc surface 21 is a convex surface, and the second arc surface 22 is a concave surface, and the concave surface extends from the top of the thread to the bottom of the thread. Figure 8 It is a second embodiment of the threaded connection, the first arc surface 21 is a concave surface, the second arc surface 22 is a concave surface, the internal thread 2 is arranged on the fastener, and the threaded connection is a reverse curved anti-loosening threaded connection, the concave surface extends from the top of the thread to the bottom of the thread, the normals of the two side surfaces of the thread of the screw 1 are opposite to each other (i.e. "back to back"), and the two side surfaces of the thread of the fastener are also concave surfaces, and the normals of the two side surfaces of the thread of the fastener are opposite to each other (i.e. "face to face"); however, the arc surfaces are still in the same direction at the thread contact surface. The threaded connection is suitable for the situation where the material strength of the screw 1 is high and the strength of the fastener is low. After the two are matched, the strength is equal and the anti-loosening effect is not reduced; for example, it is used for screws whose base plates are wood (wood is equivalent to the fastener, and the internal thread 2 is arranged on the wood) and plastic.

[0042] The third embodiment of the threaded connector: Figure 9The threaded connection member is a single-sided curved surface anti-loosening threaded connection. The surfaces where the external thread 11 and the internal thread 2 do not contact are both inclined surfaces 23. The inclined surface 23 and the first arc surface 21 are respectively arranged on both sides of the thread tooth. The first arc surface 21 is a concave surface. The thickness of the thread tooth at the tooth root is the same as the thickness of the triangular thread at the tooth root. This structural design can reduce the processing difficulty; on the premise of ensuring strength, the anti-loosening effect is also not reduced.

[0043] The fourth implementation manner of the threaded connection member: Attached Figure 10 The threaded connection member is a single-sided curved surface anti-loosening serrated threaded connection. The internal thread 2 is arranged on the fastener. The surfaces where the external thread 11 and the internal thread 2 do not contact are both inclined surfaces 23. The inclined surface 23 and the first arc surface 21 are respectively arranged on both sides of the thread tooth. The first arc surface 21 is a concave surface. The forming angle at the inclined surface 23 is 0° - 5°. This threaded connection member can be used in the case where the material strength of the screw 1 is high while the strength of the fastener is low; such as the threaded connection of the rail fastener threaded spike, where the threaded spike is a steel part (the external thread 11 is arranged on the spike), with high material strength; while the threaded embedded pipe is an engineering plastic (the internal thread 2 is arranged on the embedded pipe), with low strength. After the two are matched, the strength is equal and the anti-loosening effect is not reduced.

[0044] Finally, the method of the present invention is only a preferred implementation scheme and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0045] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A lock - loosening - resistant threaded connection against complex variable loads, characterized in that, It includes a threaded connector. The threaded connector includes a screw rod and an internal thread that mates with the external thread of the screw rod. The surfaces where the external thread and the internal thread come into contact are both first arc surfaces. The curvature radii of the two first arc surfaces are equal and the convex directions are the same. The first arc surface extends from the root to the crest of the thread tooth of the threaded connector. The thread angle increases as the transverse alternating load increases or the axial alternating load decreases, and the thread angle decreases as the transverse alternating load decreases or the axial alternating load increases.

2. The anti-loosening threaded connection against complex variable loads according to claim 1, characterized in that, By calculating the curvature radius tolerance and the curvature position tolerance of the first arc surface, the thread angle increases as the transverse alternating load increases or the axial alternating load decreases, and the thread angle decreases as the transverse alternating load decreases or the axial alternating load increases.

3. The anti-loosening threaded connection against complex variable loads according to claim 2, wherein The curvature radius tolerance and the curvature position tolerance of the first arc surface are optimized by finite element calculation.

4. The anti-loosening threaded connection against complex variable loads according to claim 3, characterized in that The specific steps for the finite element to optimize the calculation of the curvature radius tolerance and the curvature position tolerance of the first arc surface are as follows: In the finite element calculation, the initial values of the curvature radius tolerance and the curvature position tolerance of the first arc surface are both zero, and the step size is 0.2 micrometers. Then iterative calculations are carried out to ensure that the thread angle increases as the transverse alternating load increases or the axial alternating load decreases, and the thread angle decreases as the transverse alternating load decreases or the axial alternating load increases.

5. The anti-loosening threaded connection against complex variable loads according to claim 4, characterized in that, The thickness of the thread tooth at the root is the same as that of the triangular thread at the root, and the thickness of the thread tooth of the screw rod at the pitch diameter is the same as that of the internal thread.

6. The anti-loosening threaded connection against complex variable loads according to claim 4, characterized in that The surfaces where the external thread and the internal thread do not come into contact are both second arc surfaces, and the second arc surface and the first arc surface are respectively located on both sides of the thread tooth.

7. The anti-loosening threaded connection against complex variable loads according to claim 4, characterized in that, The surfaces where the external thread and the internal thread do not come into contact are both inclined surfaces. The inclined surface and the first arc surface are respectively located on both sides of the thread tooth. The first arc surface is a concave surface, and the thickness of the thread tooth at the root is the same as that of the triangular thread at the root.

8. The anti-loosening threaded connection against complex variable loads according to claim 4, characterized in that, The surfaces where the external thread and the internal thread do not come into contact are both inclined surfaces. The inclined surface and the first arc surface are respectively located on both sides of the thread tooth. The first arc surface is a concave surface, and the forming angle at the inclined surface is 0° - 5°.

Images