Internal thread and threaded connection pair

Abstract

The invention provides an internal thread and a threaded connection pair, and belongs to the technical field of threaded connection. The internal thread is a meter thread or an MJ thread, a thread profile of the internal thread comprises a thread top, a straight line section, a thread bottom and a straight line section which are connected in sequence, the thread angle of the internal thread is 60 degrees, the thread pitch is P, the thread height is hn, a groove is formed in the thread bottom of the internal thread, the groove width of the groove is defined as g, the maximum depth of the groove is hd, and then # imgabs0 is obtained. The bending deflection of the internal thread tooth is improved, at the moment, the internal thread is equivalent to a spring with reduced rigidity, and therefore when the thread connection pair bears alternating loads, the internal thread tooth can generate larger bending deformation to absorb inertia force generated by the alternating loads, and therefore the stress of the tooth bottom of the external thread under the action of the alternating loads is reduced; and the fatigue performance of the external threads is improved.

Description

Technical Field

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

[0002] In the field of engineering, thread fatigue fracture is a particularly critical technical challenge, especially in equipment and components that are subjected to high stress and long service life, and its impact cannot be ignored. As a common connection method, thread has been widely used in many industries such as automobiles, aerospace, petrochemicals, and construction. The strength and stability of the connection are directly related to the safety and reliability of the entire structure.

[0003] Currently, the common threaded connection pairs include metric threads and MJ threads. The tooth profiles of standard metric threads are as follows: Figure 1 As shown in the figure, the tooth profile of both internal and external threads includes the crest, straight line segment, root and straight line segment connected in sequence, where D is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. The crest width of the internal thread is The tooth bottom width is The crest width of the external thread is The tooth bottom width is Since the tooth angle of the internal and external threads is 60°, the tooth height of the internal and external threads can be obtained through geometric calculation. (Right now Figure 1 In ).

[0004] The tooth type of standard MJ thread is as follows Figure 2 As shown in the figure, the tooth profiles of internal and external threads also include the crest, straight line segment, root and straight line segment connected in sequence, where D is the major diameter of the internal thread, d is the major diameter of the external thread, D2 is the middle diameter of the internal thread, d2 is the middle diameter of the external thread, D1 is the minor diameter of the internal thread, d1 is the minor diameter of the external thread, P is the pitch, and H is the height of the original triangle. Unlike metric threads, the crest width of MJ internal threads is The tooth bottom width is The crest width of the MJ external thread is The tooth bottom width is Since the tooth angles of the MJ internal and external threads are both 60°, the tooth heights of the MJ internal and external threads can be obtained through geometric calculations as follows: (Right now Figure 2 In ).

[0005] At present, no matter it is metric thread or MJ thread, due to the influence of the thread structure itself, the average thickness of the external thread teeth is smaller than the average thickness of the internal thread teeth, so the stiffness of the internal thread teeth is greater than the stiffness of the external thread teeth, resulting in the threaded connection pair being subjected to alternating loads. The external thread with smaller thread stiffness acts as an energy absorption box for the internal thread with larger stiffness. The external thread teeth will produce greater bending deformation, and the adjacent external thread teeth will have a tendency to open due to the action of the internal thread. This tendency will produce a large stress concentration phenomenon at the bottom of the external thread teeth, resulting in poor fatigue performance of the external thread, and then causing the entities where the external thread is located, such as bolts, studs and other parts, to easily produce fatigue fracture, seriously affecting the safety and reliability of engineering equipment. Summary of the invention

[0006] The purpose of the present invention is to provide an internal thread to solve the problem in the prior art that the stiffness of the internal thread teeth is greater than the stiffness of the external thread teeth, resulting in poor fatigue performance of the external thread when the threaded connection pair is subjected to alternating loads, which in turn causes parts such as bolts and studs to easily suffer fatigue fractures, seriously affecting the safety and reliability of engineering equipment; the purpose of the present invention is also to provide a threaded connection pair to solve the above-mentioned problem.

[0007] To achieve the above purpose, the internal thread in the present invention adopts the following technical solution:

[0008] An internal thread, which is a metric thread or an MJ thread, wherein the tooth profile of the internal thread includes a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the tooth profile angle of the internal thread is 60°, the pitch is P, and the tooth height is h n The internal thread has a groove at its bottom, with the maximum width of the groove being g and the maximum depth being h. d ,but

[0009] The beneficial effect of the above technical solution is that: the present invention belongs to an improved invention, the improvement is that a groove is provided at the root of the internal thread, and the maximum width of the groove is g, The lower limit of g is 0.2 mm, which ensures that the existing tool can process the groove; the upper limit of g is The tooth bottom width is the standard metric internal thread or MJ internal thread, ensuring that the groove is only processed on the tooth bottom, so that the tooth height of the internal thread can be simply increased, the rigidity of the internal thread can be reduced, and the bending deflection of the internal thread can be increased. At this time, the internal thread is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread tooth bottom under the action of the alternating load, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0010] At the same time, the present invention also defines the maximum depth h d range, The lower limit This is because in actual processing, due to the structure of the tool itself, a small arc will be processed at the root of the internal thread. The tooth angle is 60°, and the depth of the small arc can be obtained by geometric calculation: A value greater than this value ensures that the groove defined in the present invention is processed separately, rather than the small arc of the tooth bottom itself. n This is because the groove cannot be too deep and the tooth height of the entire internal thread cannot be increased to more than twice the original to ensure the safety of the internal thread.

[0011] Further,

[0012] Furthermore, the internal thread is a metric thread.

[0013] Furthermore, the internal thread is an MJ thread.

[0014] Furthermore, the cross section of the groove is U-shaped.

[0015] To achieve the above purpose, the threaded connection pair in the present invention adopts the following technical solution:

[0016] A threaded connection pair includes an internal thread and an external thread used in conjunction with the internal thread. The external thread is a standard metric thread or MJ thread. The tooth profile of the internal thread includes a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence. The tooth profile angle of the internal thread is 60°, the pitch is P, and the tooth height is h. n The internal thread is a modified metric thread or MJ thread. The root of the internal thread is provided with a groove, and the maximum width of the groove is defined as g and the maximum depth is defined as h. d ,but

[0017] The beneficial effect of the above technical solution is that: the present invention belongs to an improved invention, the improvement is that a groove is provided at the root of the internal thread, and the maximum width of the groove is g, The lower limit of g is 0.2 mm, which ensures that the existing tool can process the groove; the upper limit of g is The tooth bottom width is the standard metric internal thread or MJ internal thread, ensuring that the groove is only processed on the tooth bottom, so that the tooth height of the internal thread can be simply increased, the rigidity of the internal thread can be reduced, and the bending deflection of the internal thread can be increased. At this time, the internal thread is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread tooth bottom under the action of the alternating load, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0018] At the same time, the present invention also defines the maximum depth h d range, The lower limit This is because in actual processing, due to the structure of the tool itself, a small arc will be processed at the root of the internal thread. The tooth angle is 60°, and the depth of the small arc can be obtained by geometric calculation: A value greater than this value ensures that the groove defined in the present invention is processed separately, rather than the small arc of the tooth bottom itself. n This is because the groove cannot be too deep and the tooth height of the entire internal thread cannot be increased to more than twice the original to ensure the safety of the internal thread.

[0019] Further,

[0020] Furthermore, the internal thread is an improved metric thread.

[0021] Furthermore, the internal thread is an improved MJ thread.

[0022] Furthermore, the cross section of the groove is U-shaped. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a tooth profile diagram of a standard metric thread in the prior art;

[0024] Figure 2 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0025] Figure 3 The figure is a tooth profile diagram of the internal thread embodiment 1 of the present invention;

[0026] Figure 4 Schematic diagram of the small arc at the root of the internal thread in Embodiment 1 of the present invention;

[0027] Figure 5This is a thread marking position diagram in internal thread embodiment 1 of the present invention;

[0028] Figure 6 This is a curve diagram showing the change of average stress at a calibrated position over time under the action of an alternating load in Example 1 of the internal thread of the present invention;

[0029] Figure 7 This is a tooth profile diagram of internal thread embodiment 2 of the present invention;

[0030] Figure 8 This is a curve diagram of the average stress at the calibrated position changing with time under the action of alternating load in internal thread embodiment 2 of the present invention. DETAILED DESCRIPTION

[0031] In view of the technical problems existing in the prior art, the basic inventive concept of the present invention is to process a groove at the bottom of the standard metric internal thread or MJ internal thread, thereby increasing the tooth height of the internal thread, reducing the rigidity of the internal thread teeth, and improving the bending deflection of the internal thread teeth. When the threaded connection pair is subjected to alternating loads, the internal thread teeth can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread.

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

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

[0034] The internal thread in this embodiment is a metric internal thread used in conjunction with a standard metric external thread. The tooth profile of the internal thread is evolved from the tooth profile of the standard metric internal thread. Figure 3 As shown, the tooth profile of the internal thread includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The tooth profile angle α of the internal thread is 60°, the pitch is P, the major diameter is D, the middle diameter is D2, the minor diameter is D1, and the tooth height is h n , the crest width is The tooth bottom width is These parameters are the same as those of standard metric internal threads, so according to the geometric relationship, we can find

[0035] The present invention processes a groove at the bottom of the internal thread, and defines the maximum width of the groove as g (in this embodiment, the cross section of the groove is U-shaped, and the width of the groove is equal at all places, so g can also be directly called the groove width) and the maximum depth as h. d ,but The lower limit of g is 0.2mm, considering that the groove width that can be machined by the smallest existing tool is 0.2mm, so this lower limit ensures that the existing tool can machine the groove. The upper limit of g is The standard metric internal thread root width ensures that the groove is only processed on the thread root, so that the thread height of the internal thread can be simply increased, the rigidity of the internal thread can be reduced, and the bending deflection of the internal thread can be increased. At this time, the internal thread is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread root under the action of the alternating load, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0036] At the same time, the present invention also defines the maximum depth h d range, The lower limit This is because in actual processing, due to the structure of the tool itself, a small arc will be processed at the bottom of the internal thread, such as Figure 4 As shown, the combined tooth bottom width is The tooth angle is 60°, and the depth of the small arc can be obtained through geometric calculation. A value greater than this value ensures that the groove defined in the present invention is processed separately, rather than the small arc of the tooth bottom itself. n The groove cannot be too deep and the tooth height of the entire internal thread cannot be increased to more than twice the original to ensure the safety of the internal thread. Since the internal thread in this embodiment is a metric thread, Therefore

[0037] Since the groove has a U-shaped cross section, it can be processed using conventional tools. like Figure 3 As shown in the figure, the vertical distance between the vertex of the original triangle in the metric thread profile and the major diameter D of the internal thread can be calculated by geometric calculation as h d Compare It should also be larger to ensure that the tooth height of the internal thread increases to a certain extent, thereby ensuring that the rigidity of the internal thread teeth decreases to a certain extent.

[0038] In specific applications, the pitch P of the internal thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm.

[0039] The following provides a comparative test. The specific parameters are shown in Table 1. The major diameter of the internal thread of thread 1 to thread 3 is D = 36mm, and the pitch is P = 4mm. The comparative thread is a standard metric internal thread of the same specification and pitch. By calculation, it can be known that

[0040] Among them, the groove width of the bottom groove of thread 1 to thread 3 is g = 0.4mm, and the maximum depth of the bottom groove of thread 1 is h d1 =0.3mm, Maximum depth h of the groove at the bottom of thread 2 d2 =0.433mm, Maximum depth h of the groove at the bottom of thread 3 d3 =1.5mm,

[0041] Table 1 Thread parameters in Example 1 and comparison thread

[0042] parameter Thread 1 Thread 2 Thread 3 Contrast thread P 4 4 4 4 g 0.4 0.4 0.4 / <![CDATA[h d ]]> 0.3 0.443 1.5 /

[0043] According to the above setting parameters, the dynamic analysis of the internal and external threads (the external threads used with the internal threads of the present invention and the comparative internal threads are all standard metric external threads) is performed using general finite element analysis software, that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt to obtain the external threads corresponding to threads 1 to 3 and the comparative internal threads at the calibrated position (calibrated position is Figure 5 The red dot in the figure is the first buckle position of the external thread and the internal thread, which is usually the position where the stress is most concentrated. The average stress changes with time curve at the red dot position, which is the first buckle position of the external thread and the internal thread, and is usually the position where the stress is most concentrated.

[0044] like Figure 6 As shown in Table 2, the average stress of the external threads corresponding to threads 1 to 3 at the calibrated position is smaller than the average stress of the external threads corresponding to the comparison threads at the calibrated position. Table 2 shows the stress amplitude (the difference between the maximum stress and the minimum stress on the stress curve) of the external threads corresponding to threads 1 to 3 and the comparison internal threads at the calibrated position. The smaller the amplitude, the smaller the load amplitude when the thread is subjected to the alternating load. Therefore, combined with Figure 6 It can be seen from Table 2 that the stress amplitudes of the external threads corresponding to threads 1 to 3 are smaller than those of the comparative threads, and the fatigue properties of the external threads corresponding to threads 1 to 3 are better than those of the comparative internal threads.

[0045] Table 2 Stress amplitude of the external thread corresponding to the thread in Example 1 and the comparative thread

[0046] Thread 1 Thread 2 Thread 3 Contrast thread 115.725MPa 115.314MPa 113.434MPa 116.697MPa

[0047] Embodiment 2 of the internal thread of the present invention:

[0048] The internal thread in this embodiment is an MJ internal thread used in conjunction with a standard MJ external thread. The tooth profile of the internal thread is evolved from the tooth profile of the standard MJ internal thread. Figure 7As shown, the tooth profile of the internal thread includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The tooth profile angle α of the internal thread is 60°, the pitch is P, the major diameter is D, the middle diameter is D2, the minor diameter is D1, and the tooth height is h n , the crest width is The tooth bottom width is These parameters are the same as those of the standard MJ internal thread, so according to the geometric relationship, we can find

[0049] The present invention processes a groove at the bottom of the internal thread, and defines the groove width as g (in this embodiment, the cross section of the groove is U-shaped, and the width of the groove is equal at all places, so g can also be directly called the groove width), and the maximum depth is h. d ,but The lower limit of g is 0.2mm, considering that the groove width that can be machined by the smallest existing tool is 0.2mm, so this lower limit ensures that the existing tool can machine the groove. The upper limit of g is The tooth bottom width of the standard MJ internal thread ensures that the groove is only processed on the tooth bottom, so that the tooth height of the internal thread can be simply increased, the rigidity of the internal thread can be reduced, and the bending deflection of the internal thread can be increased. At this time, the internal thread is equivalent to a spring with reduced rigidity. When the threaded connection pair is subjected to alternating loads, the internal thread can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread tooth bottom under the action of the alternating load, improving the fatigue performance of the external thread, and solving the problem that the existing external thread fatigue performance is poor, which leads to fatigue fracture of parts such as bolts and studs, seriously affecting the safety and reliability of engineering equipment.

[0050] At the same time, the present invention also defines the maximum depth h d range, The lower limit This is because in actual processing, due to the structure of the tool itself, a small arc will be processed at the root of the internal thread (same as in Example 1), combined with the root width of The tooth angle is 60°, and the depth of the small arc can be obtained through geometric calculation. A value greater than this value ensures that the groove defined in the present invention is processed separately, rather than the small arc of the tooth bottom itself. n This is because the groove cannot be too deep and the tooth height of the entire internal thread cannot be increased to more than twice the original to ensure the safety of the internal thread. Since the internal thread in this embodiment is an MJ thread, Therefore

[0051] Since the groove has a U-shaped cross section, it can be processed using conventional tools. like Figure 7As shown in the figure, the vertical distance between the vertex of the original triangle in the MJ thread profile and the major diameter D of the internal thread can be calculated by geometric calculation as h d Compare It should also be larger to ensure that the tooth height of the internal thread increases to a certain extent, thereby ensuring that the rigidity of the internal thread teeth decreases to a certain extent.

[0052] In specific applications, the pitch P of the internal thread includes but is not limited to 0.75mm, 0.8mm, 1mm, 1.25mm, 1.75mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, and 8mm.

[0053] The following provides a comparative test. The specific parameters are shown in Table 3. The major diameter of the internal thread of thread 4 to thread 6 is D = 36mm, the pitch is P = 4mm, and the comparison thread is a standard MJ internal thread of the same specification and pitch. Through calculation, it can be known that

[0054] The groove width of the groove at the bottom of thread 4 to thread 6 is g = 0.4mm, and the maximum depth of the groove at the bottom of thread 4 is Maximum depth h of the groove at the bottom of thread 5 d2 =0.433mm, Maximum depth h of the groove at the bottom of thread 6 d3 =1.5mm,

[0055] Table 3 Thread parameters in Example 2 and comparison thread

[0056] parameter Thread 4 Thread 5 Thread 6 Contrast thread P 4 4 4 4 g 0.4 0.4 0.4 / <![CDATA[h d ]]> 0.3 0.443 1.5 /

[0057] According to the above setting parameters, a general finite element analysis software is used to perform a dynamic analysis on the internal and external threads (the external threads used in conjunction with the internal threads of the present invention and the comparative internal threads are all standard MJ external threads), that is, a fixed constraint is applied to the nut, and an alternating load that changes with time is applied to the bolt to obtain a curve of the average stress change with time of the external threads corresponding to threads 4 to 6 and the comparative internal threads at the calibrated position (the calibrated position is the same as in Example 1) under the same alternating load.

[0058] like Figure 8As shown in Table 4, the average stress of the external threads corresponding to threads 4 to 6 at the calibrated position is smaller than the average stress of the external threads corresponding to the comparison threads at the calibrated position. Table 4 shows the stress amplitude (the difference between the maximum stress and the minimum stress on the stress curve) of the external threads corresponding to threads 4 to 6 and the comparison internal threads at the calibrated position. The smaller the amplitude, the smaller the load amplitude when the thread is subjected to the alternating load. Therefore, combined with Figure 8 It can be seen from Table 4 that the stress amplitudes of the external threads corresponding to threads 4 to 6 are smaller than those of the comparative threads, and the fatigue properties of the external threads corresponding to threads 4 to 6 are better than those of the comparative internal threads.

[0059] Table 4 Stress amplitude of the external thread corresponding to the thread in Example 2 and the comparative thread

[0060] Thread 4 Thread 5 Thread 6 Contrast thread 114.293MPa 114.293MPa 113.942MPa 115.396MPa

[0061] In other embodiments of the internal thread: depending on the specific shape of the tool, the cross-section of the groove can also be V-shaped, and of course it can also be arc-shaped. In these cases, the groove has a maximum width, and the maximum width position is the notch position; of course, in other embodiments, the bottom of the groove can be a straight line segment parallel to the top of the tooth in the tooth profile diagram, and the depth of the groove is equal at all locations.

[0062] In other embodiments of the internal thread: the maximum depth h d The range can also be

[0063] An embodiment of a threaded connection pair in the present invention: the threaded connection pair includes an internal thread and an external thread used in conjunction with the internal thread, the external thread is a standard metric thread or MJ thread, and the internal thread is an improved metric thread or MJ thread. The specific form of the internal thread is the same as the internal thread in the above embodiment and will not be repeated here.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the protection scope of the present invention.

Claims

1. An internal thread, which is a metric thread or an MJ thread, the tooth profile of the internal thread includes a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the tooth angle of the internal thread is 60°, the pitch is P, and the tooth height is h n , characterized in that: The bottom of the internal thread is provided with a groove, and the maximum width of the groove is defined as g and the maximum depth is defined as h. d ,but 2. The internal thread according to claim 1, characterized in that:

3. The internal thread according to claim 1 or 2, characterized in that: The internal thread is metric thread.

4. The internal thread according to claim 1 or 2, characterized in that: The internal thread is MJ thread.

5. The internal thread according to claim 1 or 2, characterized in that: The cross section of the groove is U-shaped.

6. A threaded connection pair, comprising an internal thread and an external thread used in conjunction with the internal thread, the external thread being a standard metric thread or MJ thread, the tooth profile of the internal thread comprising a tooth crest, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the tooth profile angle of the internal thread being 60°, the pitch being P, and the tooth height being h n , characterized in that: The internal thread is a modified metric thread or MJ thread. The root of the internal thread is provided with a groove, and the maximum width of the groove is defined as g and the maximum depth is defined as h. d ,but 7. The threaded connection pair according to claim 6, characterized in that:

8. The threaded connection pair according to claim 6 or 7, characterized in that: The internal thread is a modified metric thread.

9. The threaded connection pair according to claim 6 or 7, characterized in that: The internal thread is an improved MJ thread.

10. The threaded connection pair according to claim 6 or 7, characterized in that: The cross section of the groove is U-shaped.

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