Combined nut for double-end bolt and double-end bolt assembly

Abstract

The invention provides a combined nut for a double-end bolt and a double-end bolt assembly, and belongs to the technical field of bolt connection. The combined nut comprises a protective nut and a fracture nut, grooves are formed in the tooth bottoms of internal threads of the protective nut and the fracture nut respectively, the maximum width of the groove in the tooth bottoms of the internal threads of the protective nut is gb, the maximum depth of the groove in the tooth bottoms of the internal threads of the protective nut is hb, the maximum width of the groove in the tooth bottoms of the internal threads of the fracture nut is gd, and the maximum depth of the groove in the tooth bottoms of the internal threads of the fracture nut is hd. The ranges of the gd and the gb are both # imgabs 0; the ranges of the hd and the hb are both # imgabs 1 #; and meanwhile, gd.hd is less than gb.hb. The groove is formed in the tooth bottom of the internal thread, the tooth height of the internal thread is increased, the tooth rigidity of the internal thread is reduced, the tooth rigidity of the internal thread of the protection nut is smaller than that of the internal thread of the broken nut, and the internal thread of the protection nut can generate larger bending deformation to absorb inertia force generated by alternating loads. And the fatigue performance of the stud at the protective nut is improved, so that the probability that the fracture position occurs at the fracture nut is higher.

Description

Technical Field

[0001] The invention relates to a combined nut for a stud bolt and a stud bolt assembly, belonging to the technical field of bolt connection. Background Art

[0002] The stud bolt assembly is a common bolt fastener with a simple structure, easy to use, and a wide range of application scenarios. For example, the anchor bolts and blade bolt assemblies in the wind power industry are stud bolt connection structures. The blade bolts can refer to the wind turbine blade root structure and blade disclosed in the Chinese utility model patent with authorization announcement number CN202431457U, in which the blade root is pre-embedded with an embedded nut, one end of the stud bolt extends into the blade root and connects with the embedded nut, and the other end extends out of the blade root. It is fixed to the pitch flange by the fastening nut during installation. The embedded nut, fastening nut and stud bolt constitute a stud bolt assembly, and the internal thread pitch of the embedded nut and the fastening nut is equal to the external thread pitch at both ends of the stud bolt.

[0003] During the operation of a wind turbine, as the blades are stressed, the stud bolts at the root of the blades will be subjected to alternating loads such as impact and vibration. Under the action of alternating loads, the stud bolts may break in extreme cases. The fracture position of the stud bolts is random. It may break at the first thread that matches the embedded nut, or it may break at the first thread that matches the fastening nut. At present, it is impossible to accurately predict the fracture position of the stud bolts. If the fracture position of the stud bolt is located at the matching position with the fastening nut, the stud bolt still has a part that overhangs outside the blade. Using this part as the force application position, it is relatively easy to remove the remaining stud bolts from the root of the blade and then replace them with new stud bolts. However, if the fracture position of the stud bolt is located at the matching position with the embedded nut, the broken bolt head is attached to the embedded nut and located inside the blade, making it very difficult to remove, which brings great trouble to the on-site replacement operation. Of course, if the embedded nut is embedded in other structures, such as the concrete foundation under the wind turbine tower, if the embedded part of the stud bolt (also called wind turbine anchor bolt) breaks, the same technical problem exists. Summary of the invention

[0004] The object of the present invention is to provide a combination nut for stud bolts to solve the problem that the fracture position of the existing stud bolts cannot be predicted, resulting in the broken bolt head being located inside the structure when the fracture position of the stud bolt is located at the matching position with the embedded nut, which is very difficult to remove and causes great trouble to on-site replacement operations; the object of the present invention is also to provide a stud bolt assembly to solve the above-mentioned problem.

[0005] To achieve the above purpose, the combined nut for stud bolts in the present invention adopts the following technical solution:

[0006] A combination nut for stud bolts, comprising a protection nut for pre-embedded in a structure and a breaking nut for connecting with one end of the stud bolt extending outside the structure, wherein the internal threads of the protection nut and the breaking nut are both improved metric threads or MJ threads, and the tooth profiles of the internal threads both include a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, and the internal thread tooth profile angles of the protection nut and the breaking nut are both 60°, the pitches are both P, and the tooth heights are both h n The internal thread bottoms of the protection nut and the breaking nut are respectively provided with grooves, and the maximum width of the grooves at the internal thread bottoms of the protection nut is g b , the maximum depth is h b The maximum width of the groove at the bottom of the internal thread of the broken nut is g. d , the maximum depth is h d , g d and g b The range is h d and h b The range is At the same time d ·h d <g b ·h b .

[0007] The beneficial effect of the above technical solution is that: the present invention is a pioneering invention. The combined nut for stud bolts proposed in the present invention includes a protective nut and a breaking nut. The protective nut is pre-buried in the structure. The breaking nut is connected to the end of the stud bolt extending outside the structure. Measures are set to ensure that the end of the stud bolt assembly that cooperates with the protective nut will not break when subjected to alternating loads, while the end that cooperates with the breaking nut will break. Specifically, grooves are respectively provided at the bottom of the inner threads of the protective nut and the breaking nut. The maximum width of the groove at the bottom of the inner threads of the protective nut is g. b , the maximum depth is h b The maximum width of the groove at the bottom of the internal thread of the broken nut is g. d , the maximum depth is h d , g d and g b The range is The lower limit of 0.2mm ensures that the existing tool can process the groove; the upper limit The standard metric internal thread or MJ internal thread root width ensures that the groove is only processed on the root, so that the internal thread tooth height can be simply increased and the rigidity of the internal thread tooth can be reduced. d and h b The range is 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 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.

[0008] In summary, the tooth height of the internal thread of the protection nut and the broken nut in the present invention is increased, the rigidity of the internal thread can be reduced, and at the same time, due to g d ·h d <g b ·h b Therefore, the stiffness of the internal thread teeth of the protective nut will be reduced more, the stiffness of the internal thread teeth of the protective nut is less than that of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread teeth bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, which makes it easier to remove the stud bolt from the structure and facilitate on-site replacement operations.

[0009] Further,

[0010] Furthermore, the internal threads of the protection nut and the breaking nut are both improved metric threads.

[0011] Furthermore, the internal threads of the protection nut and the breaking nut are both improved MJ threads.

[0012] Furthermore, the cross section of the groove is U-shaped.

[0013] To achieve the above purpose, the combined nut for stud bolts in the present invention adopts the following technical solution:

[0014] A combination nut for stud bolts, comprising a protection nut for pre-embedded in a structure and a breaking nut for connecting with one end of the stud bolt extending outside the structure, wherein the internal thread of the breaking nut is a standard metric thread or MJ thread, the internal thread of the protection nut is an improved metric thread or MJ thread, and the tooth profile of the internal thread comprises a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, and the internal thread of the protection nut has a tooth profile angle of 60°, a pitch of P, and a tooth height of h. n The internal thread bottom of the protective nut is provided with a groove, and the maximum width of the groove is g b , the maximum depth is h b ,

[0015] The beneficial effect of the above technical solution is that: the present invention is a pioneering invention. The combined nut for stud bolts proposed in the present invention includes a protective nut and a breaking nut. The protective nut is pre-buried in the structure. The breaking nut is connected to the end of the stud bolt extending outside the structure. Measures are set to ensure that the end of the stud bolt assembly that cooperates with the protective nut will not break when subjected to alternating loads, while the end that cooperates with the breaking nut will break. Specifically, the internal thread of the breaking nut is a standard metric thread or MJ thread, while the internal thread of the protective nut is an improved metric thread or MJ thread. The improvement is that a groove is provided at the bottom of the internal thread, and the maximum width of the groove is g. b , the maximum depth is h b , The lower limit of 0.2mm ensures that the existing tool can process the groove; the upper limit The width of the tooth bottom of the standard metric internal thread or 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 and the rigidity of the internal thread can be reduced. 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 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.

[0016] In summary, in the present invention, the tooth height of the internal thread of the protective nut is increased, the rigidity of the internal thread of the protective nut can be reduced, and the broken nut does not change, so the rigidity of the internal thread of the protective nut is less than that of the broken nut, and the bending deflection of the internal thread of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture occurring at the broken nut is higher, and the stud bolt can be conveniently removed from the structure, thereby facilitating on-site replacement operations.

[0017] Further,

[0018] Furthermore, the internal thread of the protective nut is an improved metric thread.

[0019] Furthermore, the internal thread of the protective nut is an improved MJ thread.

[0020] Furthermore, the cross section of the groove is U-shaped.

[0021] To achieve the above purpose, the stud bolt assembly in the present invention adopts the following technical solution:

[0022] A stud bolt assembly comprises a stud bolt and a combination nut used in conjunction with the stud bolt, wherein the external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same, the combination nut comprises a protection nut for being embedded in a structure and a breaking nut for being connected to one end of the stud bolt extending outside the structure, the internal threads of the protection nut and the breaking nut are improved metric threads or MJ threads and the tooth profiles of the internal threads comprise a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the internal thread tooth profile angles of the protection nut and the breaking nut are both 60°, the pitches are both P, and the tooth heights are both h n The internal thread bottoms of the protection nut and the breaking nut are respectively provided with grooves, and the maximum width of the grooves at the internal thread bottoms of the protection nut is g b , the maximum depth is h b The maximum width of the groove at the bottom of the internal thread of the broken nut is g. d , the maximum depth is h d , g d and g b The range is h d and h b The range is At the same time d ·hd <g b ·h b .

[0023] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further defines that the external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same, and the combined nut includes a protective nut and a breaking nut, the protective nut is pre-buried in the structure, and the breaking nut is connected to the end of the stud bolt extending outside the structure. Measures are set to ensure that the end of the stud bolt assembly that cooperates with the protective nut will not break when subjected to alternating loads, while the end that cooperates with the breaking nut will break. Specifically, grooves are provided at the bottom of the internal threads of the protective nut and the breaking nut, respectively, and the maximum width of the groove at the bottom of the internal threads of the protective nut is g. b , the maximum depth is h b The maximum width of the groove at the bottom of the internal thread of the broken nut is g. d , the maximum depth is h d , g d and g b The range is The lower limit of 0.2mm ensures that the existing tool can process the groove; the upper limit The standard metric internal thread or MJ internal thread root width ensures that the groove is only processed on the root, so that the internal thread tooth height can be simply increased and the rigidity of the internal thread tooth can be reduced. d and h b The range is 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 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.

[0024] In summary, the tooth height of the internal thread of the protection nut and the broken nut in the present invention is increased, the rigidity of the internal thread can be reduced, and at the same time, due to g d ·h d <g b ·h bTherefore, the stiffness of the internal thread teeth of the protective nut will be reduced more, the stiffness of the internal thread teeth of the protective nut is less than that of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread teeth bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, which makes it easier to remove the stud bolt from the structure and facilitate on-site replacement operations.

[0025] Further,

[0026] Furthermore, the internal threads of the protection nut and the breaking nut are both improved metric threads.

[0027] Furthermore, the internal threads of the protection nut and the breaking nut are both improved MJ threads.

[0028] Furthermore, the cross section of the groove is U-shaped.

[0029] To achieve the above purpose, the stud bolt assembly in the present invention adopts the following technical solution:

[0030] A stud bolt assembly comprises a stud bolt and a combination nut used in conjunction with the stud bolt, wherein the external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same, the combination nut comprises a protection nut used for pre-embedded in a structure and a breaking nut used for connecting with one end of the stud bolt extending outside the structure, the internal thread of the breaking nut is a standard metric thread or MJ thread, the internal thread of the protection nut is an improved metric thread or MJ thread, and the tooth profile of the internal thread comprises a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence, the internal thread angle of the protection nut is 60°, the pitch is P, and the tooth height is h n The internal thread bottom of the protective nut is provided with a groove, and the maximum width of the groove is g b , the maximum depth is h b ,

[0031] The beneficial effect of the above technical solution is that: the present invention is an improved invention, which further defines that the external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same, and the combined nut includes a protective nut and a breaking nut, the protective nut is pre-buried in the structure, and the breaking nut is connected to the end of the stud bolt extending outside the structure, and measures are set to ensure that the end of the stud bolt assembly that cooperates with the protective nut will not break when subjected to alternating loads, while the end that cooperates with the breaking nut will break. Specifically, the internal thread of the breaking nut is a standard metric thread or MJ thread, and the internal thread of the protective nut is an improved metric thread or MJ thread, and the improvement is that a groove is provided at the bottom of the internal thread, and the maximum width of the groove is g. b , the maximum depth is h b , The lower limit of 0.2mm ensures that the existing tool can process the groove; the upper limit The width of the tooth bottom of the standard metric internal thread or 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 and the rigidity of the internal thread can be reduced. 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 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.

[0032] In summary, in the present invention, the tooth height of the internal thread of the protective nut is increased, the rigidity of the internal thread of the protective nut can be reduced, and the broken nut does not change, so the rigidity of the internal thread of the protective nut is less than that of the broken nut, and the bending deflection of the internal thread of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture occurring at the broken nut is higher, and the stud bolt can be conveniently removed from the structure, thereby facilitating on-site replacement operations.

[0033] Further,

[0034] Furthermore, the internal thread of the protective nut is an improved metric thread.

[0035] Furthermore, the internal thread of the protective nut is an improved MJ thread.

[0036] Furthermore, the cross section of the groove is U-shaped. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of embodiment 1 of the stud bolt assembly of the present invention;

[0038] Figure 2 It is a tooth profile diagram of a standard metric thread in the prior art;

[0039] Figure 3 The internal thread profile diagram of the protection nut and the broken nut in Embodiment 1 of the stud bolt assembly of the present invention;

[0040] Figure 4 It is a schematic diagram of the small arc at the bottom of the tooth in Embodiment 1 of the stud bolt assembly of the present invention;

[0041] Figure 5 It is a calibration position diagram of the stud bolt in Embodiment 1 of the stud bolt assembly of the present invention;

[0042] Figure 6 It is a curve diagram showing the change of the average stress at the calibrated position of the stud bolt 1 and the comparison bolt under the same alternating load over time in Example 1 of the stud bolt assembly of the present invention;

[0043] Figure 7 It is a curve diagram showing the change of the average stress at the calibrated position of the stud bolt 2 and the comparison bolt under the same alternating load over time in Example 1 of the stud bolt assembly of the present invention;

[0044] Figure 8 It is a curve diagram showing the change of the average stress at the calibrated position of the stud bolt 3 and the comparison bolt under the same alternating load over time in Example 1 of the stud bolt assembly of the present invention;

[0045] Fig. 9 It is a tooth profile diagram of a standard MJ thread in the prior art;

[0046] Fig.10 The internal thread profile diagram of the protection nut and the broken nut in Embodiment 2 of the stud bolt assembly of the present invention;

[0047] Fig.11 It is a curve diagram showing the change of the average stress at the calibrated position of the stud bolt 4 and the comparison bolt under the same alternating load over time in Example 2 of the stud bolt assembly of the present invention;

[0048] Fig.12It is a curve diagram showing the change of the average stress at the calibrated position of the stud bolt 5 and the comparison bolt under the same alternating load over time in Example 2 of the stud bolt assembly of the present invention;

[0049] Fig.13 The graph is a graph showing the change in average stress over time at the calibrated position of the stud bolt 6 and the comparison bolt in Example 2 of the stud bolt assembly of the present invention under the same alternating load. DETAILED DESCRIPTION

[0050] In view of the technical problems existing in the prior art, the basic inventive concept of the present invention is to divide the combination nut used in conjunction with the stud bolt into a protective nut pre-buried in the structure and a breaking nut connected to the end of the stud bolt extending outside the structure, and to design the internal thread parameters of the protective nut and the breaking nut to ensure that the internal thread teeth of the protective nut have smaller stiffness, so that when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby improving the fatigue performance of the external thread of the stud bolt at the protective nut, and making the probability of the stud bolt breaking at the breaking nut greater.

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

[0052] Embodiment 1 of the stud bolt assembly of the present invention:

[0053] like Figure 1 As shown, the stud bolt assembly includes a stud bolt 1 and a combination nut used in conjunction with the stud bolt 1, the combination nut includes a protection nut 2 for being embedded in the structure and a breaking nut 3 for being connected to one end of the stud bolt 1 extending out of the structure, the structure may be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt 1 include a protection end external thread 11 for being connected in conjunction with the protection nut 2 and a breaking end external thread 12 for being connected in conjunction with the breaking nut 3.

[0054] In this embodiment, the external thread 11 of the protection end and the external thread 12 of the breaking end are both standard metric threads, and the design parameters of the external threads at both ends are the same. The internal threads of the protection nut 2 and the breaking nut 3 are both improved metric threads, and the internal thread profiles of the protection nut 2 and the breaking nut 3 are evolved from the standard metric thread profile, so the existing standard metric thread profile is first introduced below.

[0055] like Figure 2 As shown in the figure, 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 2 In ).

[0056] In this embodiment, the internal thread profiles of the protection nut and the broken nut are the same, such as Figure 3 As shown in the figure, the tooth profile of the internal thread includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The major diameter of the internal thread of the protection nut and the broken nut is D, the middle diameter is D2, the minor diameter is D1, the tooth profile angle is α=60°, the pitch is P, and the tooth height is The width of the tooth top is

[0057] In this embodiment, the internal thread bottoms of the protection nut and the breaking nut are respectively provided with grooves, the maximum width of the grooves is g (in this embodiment, the cross section of the grooves is U-shaped, and the width of the grooves is equal everywhere, so g can also be directly called the groove width) and the maximum depth is h. For the convenience of distinction, the groove width of the internal thread bottom of the protection nut is defined as g b , the maximum depth is h b The width of the groove at the bottom of the internal thread of the broken nut is g. d , the maximum depth is h d , then g d and g b The range is The lower limit of the groove width is 0.2mm, which is based on the fact that the smallest existing tool can produce a groove with a width of 0.2mm. Therefore, this lower limit ensures that the existing tool can produce the groove. The standard metric internal thread bottom width ensures that the groove is only processed on the thread bottom, so that the thread height of the internal thread can be simply increased and the rigidity of the internal thread can be reduced.

[0058] At the same time, h d and h b The range is 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. nThe 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, so

[0059] In summary, in this embodiment, the tooth height of the internal thread of the protection nut and the broken nut is increased, the rigidity of the internal thread can be reduced, and g d ·h d <g b ·h b Therefore, the stiffness of the internal thread teeth of the protective nut will be reduced more, the stiffness of the internal thread teeth of the protective nut is less than that of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread teeth bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, which makes it easier to remove the stud bolt from the structure and facilitate on-site replacement operations.

[0060] 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 and h b Average ratio 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.

[0061] 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.

[0062] In order to better demonstrate the performance advantages of the stud bolt assembly in this embodiment, three groups of comparative tests are provided below. In the first group of comparative tests: the external threads at the protective end and the external threads at the broken end of the stud bolt 1 and the comparative bolt are both standard metric threads (for ease of description, the present invention also divides the two ends of the comparative bolt into a broken end and a protective end), the internal threads of the nuts used at both ends of the comparative bolt are both standard metric threads, and the nuts used at both ends of the stud bolt 1 are the protective nuts and broken nuts of the present invention. The major diameter of all external and internal threads is 36mm, the pitch P=4mm, and the groove width g of the internal thread bottom of the broken nut d =0.35mm, maximum depth h d =1.2mm, the groove width g of the bottom of the internal thread of the protective nut b =0.4mm, maximum depth h b =2mm, so we can know that in this group of tests: g d <g b , while h d <h b .

[0063] The general finite element analysis software is used to perform dynamic analysis on the internal and external threads. That is, a fixed constraint is imposed on the nut, and an alternating load that changes with time is imposed on the bolt. Under the same alternating load, the stud bolt 1 and the comparison bolt are at the calibrated position (the stud bolt 1 and the comparison bolt have calibrated positions at the fracture end and the protection end, and the calibrated position is Figure 5 The red dot in the figure is the first position where the bolt's external thread and the nut fit together, which is usually also the position where the stress is most concentrated. Figure 6 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, and the average stress at the fracture end and the protection end of the stud bolt 1 is less than the average stress at both ends of the comparison bolt, which shows that the fatigue performance of the stud bolt 1 is better. At the same time, since the average stress at the fracture end of the stud bolt 1 is greater than the average stress at the protection end, that is, the fatigue performance of the protection end of the stud bolt 1 is better than that of the fracture end, when fatigue fracture occurs, the bolt breaks first at the fracture end.

[0064] In the second group of comparative tests: the external threads at the protection end and the external threads at the fracture end of the stud bolt 2 and the comparative bolt are standard metric threads, the internal threads of the nuts used at both ends of the comparative bolt are standard metric threads, and the nuts used at both ends of the stud bolt 2 are the protective nuts and fracture nuts of the present invention. The major diameter of all external and internal threads is 36 mm, the pitch P = 4 mm, and the groove width g of the internal thread bottom of the fracture nut is d =0.4mm, maximum depth h d =0.8mm, the width of the groove at the bottom of the internal thread of the nut is g b=0.4mm, maximum depth h b =1.8mm, so we can know that in this group of tests: g d =g b , while h d <h b .

[0065] Similarly, the general finite element analysis software is used to perform dynamic analysis on the internal and external threads, and the average stress variation curves of the stud bolt 2 and the comparison bolt at the calibrated position under the same alternating load are obtained. Figure 7 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, and the average stress at the fracture end and the protection end of the stud bolt 2 is less than the average stress at both ends of the comparison bolt, which shows that the fatigue performance of the stud bolt 2 is better. At the same time, since the average stress at the fracture end of the stud bolt 2 is greater than the average stress at the protection end, that is, the fatigue performance of the protection end of the stud bolt 2 is better than that of the fracture end, when fatigue fracture occurs, the bolt breaks first at the fracture end.

[0066] In the third group of comparative tests: the external threads at the protection end and the external threads at the fracture end of the stud bolt 3 and the comparative bolt are both standard metric threads, the internal threads of the nuts used at both ends of the comparative bolt are both standard metric threads, and the nuts used at both ends of the stud bolt 3 are the protective nuts and fracture nuts of the present invention. The major diameter of all external and internal threads is 36 mm, the pitch P = 4 mm, and the groove width g of the internal thread bottom of the fracture nut is d =0.25mm, maximum depth h d =2mm, the width of the groove at the bottom of the internal thread of the nut is g b =0.4mm, maximum depth h b =2mm, so we can know that in this group of tests: h d =h b , while g d <g b .

[0067] Similarly, the general finite element analysis software is used to perform dynamic analysis on the internal and external threads, and the average stress variation curves of the stud bolt 3 and the comparison bolt at the calibrated position under the same alternating load are obtained. Figure 8 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, and the average stress at the fracture end and the protection end of the stud bolt 3 is less than the average stress at both ends of the comparison bolt, which shows that the fatigue performance of the stud bolt 3 is better. At the same time, since the average stress at the fracture end of the stud bolt 3 is greater than the average stress at the protection end, that is, the fatigue performance of the protection end of the stud bolt 3 is better than that of the fracture end, when fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0068] Embodiment 2 of the stud bolt assembly of the present invention:

[0069] The stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt, the combination nut includes a protection nut used to be embedded in the structure and a breaking nut used to be connected to one end of the stud bolt extending outside the structure, the structure may be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protection end external thread connected in conjunction with the protection nut and a breaking end external thread connected in conjunction with the breaking nut.

[0070] In this embodiment, the external threads of the protection end and the fracture end are both standard MJ threads, and the design parameters of the external threads at both ends are the same. The internal threads of the protection nut and the fracture nut are both improved MJ threads, and the internal thread profiles of the protection nut and the fracture nut are the same, both of which are evolved from the standard MJ thread profile, so the existing standard MJ thread profile is first introduced below.

[0071] like Fig. 9 As shown in the figure, 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 Fig.13 In ).

[0072] In this embodiment, the internal thread profiles of the protection nut and the broken nut are the same, such as Fig.10 As shown in the figure, the tooth profile of the internal thread includes the tooth top, straight line segment, tooth bottom and straight line segment connected in sequence. The major diameter of the internal thread of the protection nut and the broken nut is D, the middle diameter is D2, the minor diameter is D1, the tooth profile angle is α=60°, the pitch is P, and the tooth height is The width of the tooth top is

[0073] In this embodiment, the internal thread bottoms of the protection nut and the breaking nut are respectively provided with grooves, the maximum width of the grooves is g (in this embodiment, the cross section of the grooves is U-shaped, and the width of the grooves is equal everywhere, so g can also be directly called the groove width) and the maximum depth is h. For the convenience of distinction, the groove width of the internal thread bottom of the protection nut is defined as g b , the maximum depth is h b The width of the groove at the bottom of the internal thread of the broken nut is g. d, the maximum depth is h d , then g d and g b The range is The lower limit of the groove width is 0.2mm, which is based on the fact that the groove width that can be machined by the smallest existing tool is 0.2mm. Therefore, this lower limit ensures that the existing tool can machine the groove. The standard MJ internal thread bottom width ensures that the groove is only processed on the bottom of the thread, so that the internal thread height can be simply increased and the rigidity of the internal thread can be reduced.

[0074] At the same time, h d and h b The range is 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 (reference Figure 4 ), 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 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, so

[0075] In summary, in this embodiment, the tooth height of the internal thread of the protection nut and the broken nut is increased, the rigidity of the internal thread can be reduced, and g d ·h d <g b ·h b Therefore, the stiffness of the internal thread teeth of the protective nut will be reduced more, the stiffness of the internal thread teeth of the protective nut is less than that of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread teeth bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt suffers fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, which makes it easier to remove the stud bolt from the structure and facilitate on-site replacement operations.

[0076] Since the groove has a U-shaped cross section, it can be processed using conventional tools. like Fig.10 As 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 and h b Average ratio 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.

[0077] 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.

[0078] In order to better demonstrate the performance advantages of the stud bolt assembly in this embodiment, three groups of comparative tests are provided below. In the fourth group of comparative tests: the external threads at the protection end and the external threads at the fracture end of the stud bolt 4 and the comparative bolt are both standard MJ threads, the internal threads of the nuts used at both ends of the comparative bolt are both standard MJ threads, and the nuts used at both ends of the stud bolt 4 are the protective nuts and fracture nuts of the present invention. The major diameter of all external and internal threads is 36 mm, the pitch P = 4 mm, and the groove width g of the internal thread bottom of the fracture nut is 1.3 mm. d =0.35mm, maximum depth h d =1.2mm, the groove width g of the bottom of the internal thread of the protective nut b =0.4mm, maximum depth h b =1.8mm, so we can know that in this group of tests: g d <g b , while h d <h b .

[0079] The dynamic analysis of the internal and external threads was performed using general finite element analysis software, and the average stress variation curves of the stud bolt 4 and the comparison bolt at the calibrated position over time were obtained under the same alternating load. Fig.11 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, and the average stress at the fracture end and the protection end of the stud bolt 4 is less than the average stress at both ends of the comparison bolt, which shows that the fatigue performance of the stud bolt 4 is better. At the same time, since the average stress at the fracture end of the stud bolt 4 is greater than the average stress at the protection end, that is, the fatigue performance of the protection end of the stud bolt 4 is better than that of the fracture end, when fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0080] In the fifth group of comparative tests: the external threads at the protection end and the external threads at the fracture end of the stud bolt 5 and the comparative bolt are standard MJ threads, the internal threads of the nuts used at both ends of the comparative bolt are standard MJ threads, and the nuts used at both ends of the stud bolt 5 are the protective nuts and fracture nuts of the present invention. The major diameter of all external and internal threads is 36 mm, the pitch P = 4 mm, and the groove width g of the internal thread bottom of the fracture nut is d =0.4mm, maximum depth h d =1mm, the width of the groove at the bottom of the internal thread of the nut is g b =0.4mm, maximum depth h b =1.8mm, so we can know that in this group of tests: g d =g b , while h d <h b .

[0081] The general finite element analysis software is also used to perform dynamic analysis on the internal and external threads, and the average stress variation curves of the stud bolt 5 and the comparison bolt at the calibrated position over time under the same alternating load are obtained. Fig.12 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, and the average stress at the fracture end and the protection end of the stud bolt 5 is less than the average stress at both ends of the comparison bolt, which shows that the fatigue performance of the stud bolt 5 is better. At the same time, since the average stress at the fracture end of the stud bolt 5 is greater than the average stress at the protection end, that is, the fatigue performance of the protection end of the stud bolt 5 is better than that of the fracture end, when fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0082] In the sixth group of comparative tests: the external threads at the protection end and the external threads at the fracture end of the stud bolt 6 and the comparative bolt are standard MJ threads, the internal threads of the nuts used at both ends of the comparative bolt are standard MJ threads, and the nuts used at both ends of the stud bolt 6 are the protective nuts and fracture nuts of the present invention. The major diameter of all external and internal threads is 36 mm, the pitch P = 4 mm, and the groove width g of the internal thread bottom of the fracture nut is d =0.25mm, maximum depth h d =1.5mm, width of groove g protecting the bottom of the internal thread of the nut b =0.4mm, maximum depth h b =1.5mm, so we can know that in this group of tests: h d =h b , while g d <g b .

[0083] The general finite element analysis software is also used to perform dynamic analysis on the internal and external threads, and the average stress variation curves of the stud bolt 6 and the comparison bolt at the calibrated position over time are obtained under the same alternating load. Fig.13 As shown, the average stress at the calibrated position at both ends of the comparison bolt is equal at each moment, and the average stress at the fracture end and the protection end of the stud bolt 6 is less than the average stress at both ends of the comparison bolt, which shows that the fatigue performance of the stud bolt 6 is better. At the same time, since the average stress at the fracture end of the stud bolt 6 is greater than the average stress at the protection end, that is, the fatigue performance of the protection end of the stud bolt 6 is better than that of the fracture end, when fatigue fracture occurs, the bolt breaks preferentially at the fracture end.

[0084] Embodiment 3 of the stud bolt assembly of the present invention:

[0085] Similar to Example 1, the stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt, the combination nut includes a protective nut for being embedded in the structure and a breaking nut for being connected to one end of the stud bolt extending outside the structure, the structure can be the root of a wind turbine blade, or it can be a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected in conjunction with the protective nut and a breaking end external thread connected in conjunction with the breaking nut. At the same time, in this embodiment, the protective end external thread and the breaking end external thread are both standard metric threads, and the design parameters of the external threads at both ends are the same.

[0086] Similar to Example 1, the internal thread profiles of the protective nut and the broken nut both include a crest, a straight line segment, a root and a straight line segment connected in sequence. Different from Example 1, in this embodiment, the internal thread of the broken nut is a standard metric thread, and the internal thread root of the broken nut is not provided with a groove, while only the internal thread of the protective nut is an improved metric thread, and the internal thread root of the protective nut is provided with a groove.

[0087] The internal thread angle of the protection nut and the broken nut is 60°, the pitch is P, and the thread height is The width of the tooth top is Define the maximum width of the groove protecting the bottom of the internal thread of the nut as g. b (In this embodiment, the cross section of the groove is U-shaped, and the width of the groove is equal at all places, so it can also be directly called g b is the groove width), the maximum depth is h b , The lower limit of the groove width is 0.2mm, which is based on the fact that the groove width that can be machined by the smallest existing tool is 0.2mm. Therefore, this lower limit ensures that the existing tool can machine the groove. The standard metric internal thread bottom width ensures that the groove is only processed on the thread bottom, so that the thread height of the internal thread can be simply increased and the rigidity of the internal thread can be reduced.

[0088] At the same time, the maximum depth 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 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. The upper limit value of the maximum depth h 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 of the protective nut in this embodiment is a metric thread, so

[0089]

[0090] In summary, in the present invention, the tooth height of the internal thread of the protective nut is increased, the rigidity of the internal thread of the protective nut can be reduced, and the broken nut does not change. In addition, according to the three groups of comparative tests in Example 1, when a groove is opened at the bottom of the internal thread, the average stresses at the broken end and the protective end of the stud bolt are both less than the average stresses at both ends of the comparative bolt, so the rigidity of the internal thread of the protective nut is less than the rigidity of the internal thread of the broken nut, and the bending deflection of the internal thread of the protective nut is larger. When the stud bolt assembly is subjected to an alternating load, the internal thread of the protective nut can undergo a larger bending deformation to absorb the inertia force generated by the alternating load, thereby reducing the stress of the external thread bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt is fatigue fractured, the probability of the fracture occurring at the broken nut is higher, so that the stud bolt can be easily removed from the structure, which is convenient for on-site replacement operations.

[0091] Since the groove has a U-shaped cross section, it can be processed using conventional tools. The vertical distance between the vertex of the original triangle in the metric thread profile and the major diameter of the internal thread can be calculated by geometric calculation as h b 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.

[0092] Embodiment 4 of the stud bolt assembly of the present invention:

[0093] Similar to Example 2, the stud bolt assembly in this embodiment also includes a stud bolt and a combination nut used in conjunction with the stud bolt, the combination nut includes a protective nut for being embedded in the structure and a breaking nut for being connected to one end of the stud bolt extending outside the structure, and the structure can be the root of a wind turbine blade or a concrete foundation under a wind turbine tower. The external threads at both ends of the stud bolt include a protective end external thread connected in conjunction with the protective nut and a breaking end external thread connected in conjunction with the breaking nut. At the same time, in this embodiment, the protective end external thread and the breaking end external thread are both standard MJ threads, and the design parameters of the external threads at both ends are the same.

[0094] Similar to Example 2, the internal thread profiles of the protective nut and the broken nut both include a crest, a straight line segment, a root and a straight line segment connected in sequence. Different from Example 2, in this embodiment, the internal thread of the broken nut is a standard MJ thread, and the internal thread root of the broken nut is not provided with a groove, while only the internal thread of the protective nut is an improved MJ thread, and the internal thread root of the protective nut is provided with a groove.

[0095] The internal thread angle of the protection nut and the broken nut is 60°, the pitch is P, and the thread height is The width of the tooth top is Define the maximum width of the groove protecting the bottom of the internal thread of the nut as g. b (In this embodiment, the cross section of the groove is U-shaped, and the width of the groove is equal at all places, so it can also be directly called g b is the groove width), the maximum depth is h b , The lower limit of the groove width is 0.2mm, which is based on the fact that the smallest existing tool can produce a groove with a width of 0.2mm. Therefore, this lower limit ensures that the existing tool can produce the groove. The standard MJ internal thread bottom width ensures that the groove is only processed on the bottom of the thread, so that the internal thread height can be simply increased and the rigidity of the internal thread can be reduced.

[0096] At the same time, the maximum depth 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 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. The upper limit value of the maximum depth h 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 of the protective nut in this embodiment is an MJ thread, so

[0097]

[0098] In summary, the tooth height of the internal thread teeth of the protective nut in the present invention is increased, the rigidity of the internal thread teeth of the protective nut can be reduced, and the broken nut does not change. In addition, according to the three groups of comparative tests in Example 2, when a groove is opened at the bottom of the internal thread teeth, the average stresses at the broken end and the protective end of the stud bolt are both less than the average stresses at both ends of the comparative bolt, so the rigidity of the internal thread teeth of the protective nut is less than the rigidity of the internal thread teeth of the broken nut, and the bending deflection of the internal thread teeth of the protective nut is larger. Therefore, when the stud bolt assembly is subjected to alternating loads, the internal thread teeth of the protective nut can undergo greater bending deformation to absorb the inertia force generated by the alternating loads, thereby reducing the stress of the external thread teeth bottom of the stud bolt at the protective nut, and improving the fatigue performance of the external thread of the stud bolt at the protective nut. Therefore, when the stud bolt undergoes fatigue fracture, the probability of the fracture position occurring at the broken nut is higher, and the stud bolt can be conveniently removed from the structure, facilitating on-site replacement operations.

[0099] Since the groove has a U-shaped cross section, it can be processed using conventional tools. The vertical distance between the vertex of the original triangle in the MJ thread profile and the major diameter of the internal thread can be calculated by geometric calculation as follows: h b 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.

[0100] In other embodiments of the stud bolt assembly: 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.

[0101] In other embodiments of the stud bolt assembly: when the internal thread roots of the protection nut and the breaking nut are both provided with grooves, the maximum depth of the groove at the internal thread root of the breaking nut is h d The maximum depth h of the groove at the bottom of the inner thread of the protective nut b The range can be

[0102] In other embodiments of the stud bolt assembly: when only the internal thread root of the protective nut is provided with a groove, the maximum depth of the groove at the internal thread root of the protective nut is h b The range can be

[0103] The embodiment of the combination nut for stud bolts in the present invention is as follows: the specific structure of the combination nut for stud bolts is the same as the combination nut in any embodiment of the stud bolt assembly described above, and will not be repeated here.

[0104] 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. A combination nut for a stud bolt, characterized in that: It includes a protective nut used for pre-embedded in the structure and a breaking nut used for connecting with the end of the stud bolt extending outside the structure. The internal threads of the protective nut and the breaking nut are improved metric threads or MJ threads, and the tooth profiles of the internal threads include a tooth top, a straight line segment, a tooth bottom and a straight line segment connected in sequence. The internal thread tooth angles of the protective nut and the breaking nut are both 60°, the pitches are both P, and the tooth heights are both h n The internal thread bottoms of the protection nut and the breaking nut are respectively provided with grooves, and the maximum width of the grooves at the internal thread bottoms of the protection nut is g b , the maximum depth is h b The maximum width of the groove at the bottom of the internal thread of the broken nut is g. d , the maximum depth is h d , g d and g b The range is h d and h b The range is At the same time d ·h d <g b ·h b .

2. The combination nut for stud bolts according to claim 1, characterized in that:

3. The combination nut for stud bolts according to claim 1 or 2, characterized in that: The internal threads of the protection nut and the breaking nut are improved metric threads.

4. The combination nut for stud bolts according to claim 1 or 2, characterized in that: The internal threads of the protection nut and the breaking nut are both improved MJ threads.

5. The combination nut for stud bolts according to claim 1 or 2, characterized in that: The cross section of the groove is U-shaped.

6. A combination nut for a stud bolt, characterized in that: It includes a protective nut used for pre-embedded in the structure and a breaking nut used for connecting with one end of the stud bolt extending outside the structure. The internal thread of the breaking nut is a standard metric thread or MJ thread. The internal thread of the protective nut is an improved 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 of the protective nut is 60°, the pitch is P, and the tooth height is h. n The internal thread bottom of the protective nut is provided with a groove, and the maximum width of the groove is g b , the maximum depth is h b , 7. The combination nut for stud bolts according to claim 6, characterized in that:

8. The combination nut for stud bolts according to claim 6 or 7, characterized in that: The internal thread of the protective nut is an improved metric thread.

9. The combination nut for stud bolts according to claim 6 or 7, characterized in that: The internal thread of the protective nut is an improved MJ thread.

10. The combination nut for stud bolts according to claim 6 or 7, characterized in that: The cross section of the groove is U-shaped.

11. A stud bolt assembly, comprising a stud bolt and a combination nut used in conjunction with the stud bolt, characterized in that: The external threads at both ends of the stud bolt are standard metric threads or MJ threads and the design parameters of the external threads at both ends are the same. The combination nut is the combination nut for stud bolts described in any one of claims 1 to 5 or the combination nut for stud bolts described in any one of claims 6 to 10.

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