A nut self-locking method and its self-locking structure

Abstract

The present invention provides a nut self-locking method that secures the nut to the bolt by disrupting its threading path. By controlling the thickness of the nut, the nut is continuously torqued during assembly, destroying the external threads on the bolt that mate with the nut while preserving the internal threads. When the nut is tightened, the reaction force of the connected component causes the bolt threads to break free, shearing the threads and filling the nut's thread grooves, preventing the nut from exiting the bolt and thus achieving self-locking.

Description

Technical Field

[0001] The invention relates to a nut self-locking method and a self-locking structure thereof. Background Art

[0002] Threaded connections are a common connection method for modern structures and mechanical equipment. While generally self-locking, they can become loose under varying loads, impact, vibration, and significant fluctuations in operating temperature, leading to a decrease in preload. Threaded connection practices, anti-loosening performance tests, and fatigue strength tests have shown that loosening failure is one of the primary failure modes for threaded connections subjected to alternating loads. Loosening of threaded connections will reduce or even eliminate the preload, reducing the quality of the connection, leading to premature damage to the various parts involved, and even causing the connection to become loose. In actual applications, equipment and personal accidents caused by loose or falling connectors are common. Therefore, preventing threaded connections from becoming loose is an important prerequisite for ensuring the safe operation of equipment.

[0003] Current methods for securing bolts and nuts against loosening generally include friction, mechanical, and permanent locking. Permanent locking involves friction and is non-removable, while mechanical locking involves removable locking. Common mechanical locking methods include retaining washers and slotted nut cotter pins. However, cotter pins do not effectively secure the nut against the connecting piece. Permanent locking methods include spot welding, riveting, punching, and bonding, but these methods prevent the nut from being disassembled. Common friction locking methods include spring washers, butt nuts, capped nuts, and non-metallic embedded nuts. However, these methods can cause the nut to loosen due to elastic failure and vibration.

[0004] In order to make the nut self-lock on the bolt and prevent it from loosening, a self-locking fastening structure is disclosed in publication number CN210218375U. The threaded section of the bolt and the nut are tightened to a limit, and force is applied again until the connecting section between the first threaded section and the second threaded section is broken. The bolt is fixed in the nut by using the structure in which the front and rear teeth of the first threaded section and the second threaded section exert force on each other. After the bolt and the nut are connected, they become one, making the assembly process of the components to be tightened simpler and the structure more stable. Although this method fixes the nut on the bolt, the thread between the nut and the bolt is completely destroyed, making the nut impossible to disassemble. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a nut self-locking method and a self-locking structure thereof.

[0006] The present invention is achieved through the following technical solutions.

[0007] The present invention provides a self-locking method for a nut, which fixes the self-locking nut on the bolt by destroying the screwing path of the self-locking nut on the bolt. The method is as follows:

[0008] By controlling the thickness of the self-locking nut, during the assembly process of the self-locking nut and the bolt, the external thread on the bolt that matches the nut is destroyed while the internal thread of the nut is not destroyed by continuously applying torque to the self-locking nut.

[0009] Before assembling the self-locking nuts and bolts, a standard nut is first used to apply a clamping force to the connection piece.

[0010] The thickness calculation process of the self-locking nut is:

[0011] Normal stress in the bolt thread shank: σ 杆 =F / A 杆 ;

[0012] The shear force on a single thread is Fs = F / Z;

[0013] Bolt thread shear stress τ 外纹 =3 / 2Fs / A 外纹 =1.5F / ZA 外纹 ;

[0014] Equivalent shear stress of bolt thread

[0015]

[0016] Equivalent shear stress area of bolt thread

[0017] The relationship between the shear stress of the bolt thread and the normal stress of the bolt screw is:

[0018]

[0019]

[0020]

[0021]

[0022]

[0023] Get ZA′ 外纹 =A 杆 (1);

[0024] A 杆 =π / 4d3 2 ,

[0025] d3=d1-H / 6,

[0026] d1=d-1.0825P,

[0027] A杆 =π / 4d3 2 =π(0.25d 2 -0.613dP+0.3763P 2 ) (2);

[0028] ZA′ 外纹 =0.385×0.75P×(d-1.0825P)Zπ=0.28875P(d-

[0029] 1.0825P)Zπ(3);

[0030] Substitute (2) and (3) into (1):

[0031] So π0.28875(d-1.0825P)ZP=(0.25d 2 -0.6134dP+0.3763P 2 )π(4);

[0032] In standard bolts, the relationship between pitch P and major diameter d of external thread is commonly used: 6P≤d≤9P,

[0033] Substituting the relationship into formula (4), we can obtain the minimum number of standard nut thread turns to ensure that the bolt thread is not damaged during the tightening process of the standard nut:

[0034] When d=6P, Z=4,

[0035] When d = 9P, Z = 6.6;

[0036] The thickness of the self-locking nut is H 自锁 for:

[0037] H 自锁 <ZP;

[0038] In the above formula: d1 thread minor diameter, H original triangle height, d external thread major diameter, P pitch, Z nut and bolt engagement number, D internal thread major diameter, σ 杆 Bolt screw normal stress, τ 外纹 Bolt thread shear stress, A 杆 Bolt screw stress area, A′ 外纹 , the equivalent shear stress area of a single thread of the bolt, F is the clamping force, Fs is the shear force on a single thread, A 外纹 is the stress area of a single external thread of the bolt.

[0039] During the assembly process of the bolt and the self-locking nut, the torque gradually increases from zero and then suddenly drops to zero, and the self-locking nut completes self-locking.

[0040] When the self-locking nut is disassembled, the self-locking nut is withdrawn by disassembling the standard nut.

[0041] A nut anti-loosening structure comprises a bolt and a self-locking nut. The self-locking nut is fixed on the bolt through a self-locking area.

[0042] A clamping member is also installed on the bolt to apply a clamping force to the connected member.

[0043] The self-locking area is formed by the thread on the bolt being broken off and broken, and the thread is filled in the thread groove of the self-locking nut after being broken off and broken.

[0044] The beneficial effect of the present invention is that when the nut is rotated and tightened, the reaction force of the connected part causes the bolt thread to be disengaged, the thread is cut off and filled in the nut thread groove, so that the nut cannot be withdrawn from the bolt, and the nut is self-locked. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural schematic diagram of the present invention;

[0046] Figure 2 This is a schematic diagram of the stress analysis of the bolt and nut threads of the present invention;

[0047] Figure 3 This is a schematic diagram of plane stress analysis of the bolt and nut threads of the present invention;

[0048] Figure 4 This is a schematic diagram of the normal stress distribution law of thread bending of the present invention;

[0049] Figure 5 Schematic diagram of shear stress distribution law of the present invention;

[0050] Figure 6 A schematic structural diagram of embodiment 1 of the present invention;

[0051] Figure 7 A schematic structural diagram of embodiment 2 of the present invention;

[0052] Figure 8 Schematic diagram of the structure of a clamping type self-locking nut according to embodiment 3 of the present invention;

[0053] Figure 9 This is a physical picture of the bolt thread being sheared off and filling the thread groove of the self-locking nut;

[0054] Figure 10 This is a physical picture of the bolt thread after it has been sheared off;

[0055] In the figure: 1-bolt, 2-clamping part, 3-self-locking nut, 4-self-locking area, 5-part to be connected, 6-locking nut, 7-spring washer, 8-outer ring groove, 9-inner ring groove. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0057] like Figure 1 As shown, a nut self-locking structure provided by the present invention includes a bolt 1, a clamping member 2, and a self-locking nut 3, and is characterized in that the clamping member 2 and the self-locking nut 3 are installed on the bolt of the bolt 1, and the self-locking nut 3 is fixed on the bolt 1 through the self-locking area 4.

[0058] The self-locking area 4 is formed by the thread on the bolt 1 being broken off.

[0059] The thread is broken and then filled into the thread groove of the self-locking nut 3 .

[0060] Example 1, as Figure 6 As shown, in order to ensure that the part to be connected 5 is clamped, a standard locking nut 6 is used as the clamping part 2. During the installation process, the locking nut 6 is first assembled on the bolt 1. The locking nut and the end of the bolt lock the part to be connected 5, and then the self-locking nut 3 is installed. The self-locking nut 3 is assembled to the locking nut 6 and contacts the locking nut 6. Then, the torque is continued to be applied to gradually increase the reaction force between the self-locking nut 3 and the locking nut 6. When the reaction force is greater than the shear stress of the thread on the bolt 1, the thread on the bolt 1 that cooperates with the self-locking nut 3 is cut off to form a self-locking area 4. In the self-locking area 4, the external thread of the bolt is squeezed into the nut thread groove, so that the nut cannot be withdrawn, so that the self-locking nut is locked on the bolt and will not loosen.

[0061] Example 2, as Figure 7 As shown, a spring washer 7 is used as a clamping member 2. During the installation process, the spring washer 7 is first assembled on the bolt 1, and then the self-locking nut 3 is installed. The self-locking nut 3 is assembled to the spring washer 7 and contacts the spring washer 7. Then, the torque is continued to be applied to gradually increase the reaction force between the self-locking nut 3 and the spring washer 7. When the reaction force is greater than the shear stress of the thread on the bolt 1, the thread on the bolt 1 that cooperates with the self-locking nut 3 is cut off to form a self-locking area 4. In the self-locking area 4, the external thread of the bolt is squeezed into the thread groove of the nut, so that the nut cannot be withdrawn, so that the self-locking nut is locked on the bolt and will not loosen. Since the standard nut is not installed, the self-locking nut cannot be disassembled in this installation method.

[0062] Example 3, as Figure 8As shown, the clamping part 2 and the self-locking nut 3 are processed into an integrated structure, wherein the clamping part 2 is processed according to the specification process of the standard nut, the hexagonal size of the clamping part 2 is larger than the hexagonal size of the self-locking nut 3, and the inner and outer ends of the connection between the two are respectively processed with an inner ring groove 9 and an outer ring groove 8. When the connecting part 5 is to be connected, the integrated structure formed by the clamping part 2 and the self-locking nut 3 can be assembled on the bolt 1 at the same time only by applying torque to the self-locking nut 3. When the clamping force is sufficient, the connection between the inner and outer ring grooves between the two will be twisted off, so that the clamping part 2 and the self-locking nut 3 are separated, and the self-locking nut 3 continues to rotate to cut off the thread on the bolt 1 and fill its thread groove, so that the self-locking nut 3 is fixed on the bolt.

[0063] Example 4. In the above examples 1 and 3, after the self-locking nut is assembled, if it is necessary to separate the parts to be connected later, the clamping part 2 can be disassembled and a thrust can be applied to the self-locking nut through the clamping part 2 to make it withdraw from the bolt.

[0064] The present invention is based on the fact that the shear area of the nut thread is larger than that of the bolt thread in the actual bolt-nut structure. When the number of effective turns of the bolt thread exceeds ZP, the shear area is larger than the area of the screw. By reducing the effective thickness of the nut, when the bolt thread is connected to the bolt thread, the bolt thread is sheared by the nut thread under the action of axial force. The sheared tooth metal is squeezed into the nut thread groove, preventing the nut from loosening. This makes the nut similar to a flat washer and achieves the purpose of preventing loosening.

[0065] 1. Calculation of equivalent stress area of bolt shank, bolt thread and nut thread.

[0066] When the bolt and nut are engaged, the bolt is subjected to axial tension. The force analysis of the thread teeth is to regard the thread teeth as a cantilever beam structure, and the force on the tooth side is uniform. Figure 2 、 Figure 3 According to the transverse bending theory, the thread is subjected to bending normal stress and shear stress when subjected to axial load. Figure 4 、 Figure 5 In the presence of both normal stress and shear stress, analysis is performed based on the fourth strength theory.

[0067] 4th Strength Theory σ s :Yield strength M:Bending moment=0.270625PF s σ=My / IzT=Fs / 2Iz(H 2 / 4-y 2 ), Fs=F / Z, Iz: moment of inertia, Iz=bh 3 / 12, (h is tooth thickness, b is thread length) Figure 5 .

[0068] Substitute σ and τ into (1) and find out when y = rFinite value, let dσ r / dy=0, so y=0, that is, σ=My / I=0, T=3 / 2F s / bh, further derivation can prove that d 2 σ r / dy 2 When y=0, d 2 σ r / dy 2 <0, indicating τ max =3 / 2Fs / bh, when y=0,

[0069] According to material mechanics, the present invention uses the maximum shear stress τ=3 / 2Fs / bh to check the strength, and experiments have proved that the theoretical deduction of τ=3 / 2Fs / bh is correct.

[0070] 1) Normal stress of the bolt (nail) threaded rod, σ=F / A 杆 , according to HB6443 "General Specification for Nuts" A 杆 =π / 4d3 2 , d3=d1-H / 6.

[0071] d1: thread diameter, H original triangle height, d1 = d-1.0825P.

[0072] d: major diameter of thread, P pitch.

[0073] A 杆 =π / 4d3 2 =π(0.25d 2 -0.6134dP+0.3763P 2 ) (1)

[0074] 2) Bolt (nail) thread shear stress:

[0075] τ 外纹 =3 / 2Fs / A 外纹 ,

[0076]

[0077] Equivalent shear stress area of bolt thread:

[0078]

[0079] Fs=F / Z,

[0080] ZA′ 外纹 =0.385×0.75P×(d-1.0825P)Zπ=0.28875P(d-

[0081] 1.0825P)Zπ(4).

[0082] Z: Number of engagement turns between nut and bolt.

[0083] 3) Nut shear stress: The equivalent shear stress area of the nut,

[0084] A′ 内纹 =0.28875PDZπ

[0085] τ 母 : nut thread shear stress, A′ 内纹 Equivalent shear stress area of a single internal thread of a nut, A 内纹 is the shear stress area of a single internal thread of the nut, and D is the major diameter of the internal thread.

[0086] D = d, so A 内纹 >A 外纹 , A′ 内纹 >A′ 外纹 When the nut thread and the bolt thread have the same number of engagement turns and are subjected to the same axial force, the shear stress of the nut thread is less than that of the bolt thread.

[0087] We first calculate the area of the bolt shank and the external thread, and the maximum number of turns that the thread can be disengaged without the bolt shank breaking.

[0088] According to formula (3)

[0089] Get ZA′ 外纹 =A 杆

[0090] π(0.28875(d-1.0825P)ZP=(0.25d 2 -0.6134dP+0.3763P 2 )π

[0091] (5).

[0092] The relationship between pitch and major diameter of thread recommended by conventional thread standards is: 6P≤d≤9P.

[0093] When d=6P, Z=4 turns

[0094] When d = 9P, Z = 6.6 turns. When d = 6 to 9P, the specific value of Z can be calculated using formula (5). In fact, Z takes a value of 4 to 6.6 turns.

[0095] As long as the number of engagement turns is less than 4 turns (d=6P) or less than 6.6 turns (d=9P), when the nut is rotated and tightened, the reaction force of the connected parts will cause the bolt thread to be disengaged and the threaded screw to be sheared off. 4 or 6.6 turns is the critical number of turns for bolt disengagement. The metal of the bolt's external thread teeth squeezes into the nut's thread groove, making the nut unable to withdraw, resulting in a self-locking phenomenon that will not loosen. The principle of self-locking nuts that self-lock and do not loosen is shown in the following figure. Figure 1 .

[0096] 2. When the nut is tightened, the external thread of the bolt is subjected to axial force. When the external thread of the bolt is subjected to shear stress τ 外纹 Greater than shear strength τ b The threads on the bolts are broken.

[0097] When the nut is tightened, the bolt is subjected to tension between the interlayer (connected part) and the nut, and the bolt gradually stretches and produces elastic deformation. Under the axial tension of the nut's internal thread, the external thread of the bolt also produces elastic deformation. As the nut continues to be tightened, the bolt continues to deform. However, since the number of engagement threads of the external thread is less than the critical number of turns, such as 4 turns (d = 6P) or 6.6 turns (d = 9P), when the shear stress on the external thread is greater than the shear yield stress τs of the bolt thread, the external thread first produces extrusion plastic deformation, and the thread teeth bend and deform. As the plastic deformation increases, the material hardening in the deformation zone intensifies. If torque is continued to be applied to tighten, the shear stress will be greater than the shear strength τ b When the bolt thread is applied, a small crack is generated at the small diameter rod part. Under the action of shear stress, the crack continues to expand, separating the thread from the screw at the root d1 circumference. The separated metal squeezes into the thread groove inside the nut. Figure 9 Because the effective number of threads in the self-locking nut of the present invention is less than the critical number Z, and the internal threads are filled with metal, similar to a flat washer, the external threads are sheared by the axial shear stress, while the bolt stress at this time is less than or equal to the bolt's yield strength σs.

[0098] Self-locking nut test verification

[0099] 1) The self-locking nut test is shown in Tables 1 to 4. From Table 1, we know that as the thickness of the nut increases, the maximum torque increases. This is because the increase in the number of screw turns increases the thread area and the axial force it bears. According to the relationship between torque and preload (or clamping force), T = (KFd × 10 -3)T: Torque, Nm. K: Torque coefficient, generally taken as 0.1-0.2. When lubricated with oil, K is taken as the lower limit, and when not lubricated, the upper limit is taken. d: Major diameter of thread in mm. F: Clamping force. When K and d are constant, F and T are linearly related. In our test, M6×50 bolts with strength level 8.8 and standard nuts GB6170M6 with strength level 8 were measured without oil, and K≈0.189 was measured, while when oiled, K≈0.176. For 12.9-grade M6×40 bolts and M6 nuts with strength level 8, K≈0.205 was measured without oil. The difference between oiling and not oiling is not significant. This empirical formula actually assumes that the nut thickness H≥0.8D. When torsion occurs, the bolt shank undergoes elastic deformation, while both the external thread of the bolt and the internal thread of the nut bend. The bending deformation is very small, and the deformation is mainly due to the deformation of the bolt shank. The empirical formula holds true when the stress σ≤σs.

[0100] The design thickness H of the self-locking nut is less than the critical number of turns ZP. When d=6P, H=(2~3)P, which is less than 4 turns. When d=9P, H=(3~5)P, which is less than 6.6 turns.

[0101] In the test, when the external thread of the bolt is τ<Ts (shear yield strength), the relationship between F and T is basically linear. However, when the external thread of the bolt undergoes plastic deformation when τ≥τs, the clamping force basically increases slightly, while the torque continues to rise. The increase in torque is caused by the resistance of the external thread of the bolt to the deformation caused by the extrusion of the internal thread of the nut. When the torque is further increased (i.e., the self-locking nut is screwed), the bolt shank basically does not stretch, but the external thread of the bolt continues to deform. The external thread is subjected to axial force, causing the shear stress at the minor diameter of the shank to be greater than τ. b Micro cracks are generated until they are squeezed and sheared, such as Figure 10 The picture shows the actual object after the bolt thread is sheared off.

[0102] Tables 2 and 4 show that when the axial force (clamping force) caused by torque-induced nut rotation reaches the point where the bolt's external threads yield, the torque increases while the clamping force remains essentially unchanged or increases slightly. For nut thicknesses greater than 2.5 mm, the clamping force reaches 10.7 kN at a torque of approximately 13.63 Nm, and the external threads begin to yield.

[0103] When the clamping force F = 10.7KN, the normal stress of the threaded rod is σ = 10.7 / 18.98 = 563MPa

[0104] The actual shear stress on the bolt thread is τ = 3 / 2 × 10.7 / (πd1 × 0.75Px2.5) = 554 MPa, and the measured tensile strength of the bolt is σb = 1100 MPa.

[0105] The yield strength of the bolt shank, σs, is ≥ 0.8σb, ≈ 880 MPa. The external thread experiences a shear yield strength, τs, of 0.6σs, or 528 MPa. The bolt shank is within the elastic range, while the thread is within the yield deformation range, resulting in plastic deformation. When the nut thickness is 2.0 mm and the clamping force, F, is 9.36 kN, the bolt experiences a normal stress, σ, of 9.36 / 18.98, or 493 MPa, placing the bolt shank within the elastic range. The actual shear stress on the bolt thread, τ, is 3 / 2 × 9.36 / (πd1 × 0.75P × 2) = 606 MPa, reaching the yield point and causing the thread to yield. The theoretical calculations agree closely with the experimental results.

[0106] 2) From the formula, we know that τ=F / 0.28875P(d-1.0825P)zπ. By adjusting the number of meshing circles Z, the shear stress τ can be adjusted. This test uses M6×1 bolts and nuts, and their connection meets the condition of d=6P. See Tables 1 to 4. When the torque reaches 20.2Nm at H4.0, the bolt shank breaks. The measured strength of the bolt is σb1000MPa. The force value is F=1000×18.98=18980. The torque is calculated as T=KFd×10 -3 =0.176×18980×6×10 -3 =20.0Nm, which verifies the correctness of the critical number of turns! By designing the thickness H of the self-locking nut 自锁 , the torque can be adjusted. The clamping force still depends on the standard nut (see Figure 6 ) or clamping type self-locking nut, (see Figure 8 Therefore, H is generally set to (2.0-3)P, meaning 2-3.0 turns. As can be seen from the table, for the bolt shank, σ<σs is within the elastic range, and the external thread is within the yield range. If clamping force is desired, a higher torque can be applied to the standard nut to adjust the clamping force. The design combination should be tailored to the strength of the bolt and nut. Self-locking nuts can be designed with different thread thicknesses to ensure this.

[0107] Standard nuts for clamping (e.g., H ≥ 0.8D) must meet the pull-off force requirements of GB943-88 "Technical Specifications for Self-locking Nuts," HB7595 "General Specification for Self-locking Nuts for Threads Operating Temperatures Not Exceeding 425°C," and GB / T30982-2010 "Mechanical Properties of Nuts for Fasteners."

[0108] Moreover, the standard nut plus the self-locking nut can bear a greater tensile force value. When the standard nut is tightened with a pre-tightening force, the thickness of the standard nut is generally H≥0.8D. If the internal thread is formed by cold extrusion, the hardness of the thread surface is increased. The thread streamline is continuous and not cut off. The control of the tightening pre-tightening force will be better. At the same time, the installation torque of the standard nut can be adjusted according to requirements, or the method of adjusting the rotation angle of the nut or the yield tightening method can be adopted, etc. The manufacturing process and heat treatment of the standard nut or bolt are completely manufactured according to the standard requirements. At the same time, check the major diameter of the bolt and the minor diameter of the nut. The standard nut can fully meet the standard force value requirements. Coupled with the force value contributed by the self-locking nut, the self-locking combined nut (standard nut + self-locking nut) is more secure!

[0109] 3) For the connecting nut without the requirement of clamping force, H<ZP (Z: critical number of turns, P: pitch) can be used for locking to achieve the purpose of non-loosening. When using the clamping type self-locking nut, the clamping force can be adjusted by the width of the fracture groove. There is no need to control the clamping force with a torque wrench. After the fracture groove is broken, continue to twist S2 until the torque reaches zero, and the installation of the clamping type self-locking nut is completed. The length L of S1 is L≥0.8D, and the H of S2 is less than the critical number of turns ZP.

[0110] Table 1 Torque experiment of self-locking nut with thickness 1.5 - 4.0 on M6 bolt

[0111] Table 1

[0112]

[0113]

[0114] Table 2

[0115]

[0116]

[0117] Table 3 Torque experiment results of using standard M6 nut HRC23 - 26 and self-locking nut with thickness 2.0 - 3.0 HRC23 - 26, bolt using M6×50 8.8 - grade bolt HRC25 - 27:

[0118] Table 3

[0119]

[0120]

[0121] For Table 2 and Table 4, the clamping force is measured by a resistance strain gauge sensor. The resistance strain gauge sensor is calibrated on an electronic tensile (compressive) testing machine.

[0122] Table 4

[0123]

[0124]

[0125] 2. Vibration test:

[0126] Self-locking nuts, because the internal thread groove is squeezed and filled by the metal of the bolt thread tooth, basically like a flat washer embedded in the axial groove of the bolt tooth, see Figure 9 、 Figure 10 The nut has lost its screw-on function, and the self-locking nut will not back out of the bolt, resulting in a non-loose nut. The present invention conducts a vibration test on the locking strength of the self-locking nut assembly. The vibration test is carried out in accordance with the national standard GJB715.3 "Fastener Test Method Vibration" using sinusoidal vibration with a vibration frequency of 30 Hz, a full amplitude of (11.43 ± 0.4) mm, and a cycle of 30,000 times.

[0127] The test results are shown in Table 5. The self-locking nut alone loosened because the final torque was zero and there was no friction. The standard spring washer combination did not loosen, with only a few degrees of rotation. The combination of the standard nut and the self-locking nut provided the best results, achieving no loosening at all. This met the standard requirements.

[0128] Table 5

[0129]

[0130] The test bolts are 8.8 grade M6×50, HRC25~27, the test standard nuts and self-locking nuts are M6HRC23~26, and the connection with fasteners in the combination of serial numbers 1 and 2 fully meets the design requirements.

[0131] 3. Disassembly

[0132] Existing fixed nuts are generally not disassembled and can only be disassembled by destruction, such as the methods such as the punching method spot welding, riveting bonding described above, and even the aviation standard adopts the closing to increase the friction locking type high lock nut and can only be disassembled destructively. The self-locking nut of the present invention is disassembled by utilizing the standard nut thread number (thickness H≥0.8D) to be greater than the self-locking nut number of turns. When disassembling the standard nut, because the number of turns of the standard nut is greater than the self-locking nut number of turns, when the nut passes through the self-locking zone 4, the standard nut will apply a thrust to the self-locking nut to make it translate, because there is tolerance in the nut internal thread, bolt, and external thread, and cutting off the bolt external thread during translation will leave a shallow thread groove. The standard nut continues to push along the shallow thread groove path under the exit torque effect, and the self-locking nut translates to the bolt. So the self-locking nut is about to be pushed out of the bolt with a wrench to make it detachable. When the standard nut is withdrawn with a wrench, the self-locking nut is subjected to thrust, and the self-locking nut is pushed out of the bolt, and disassembly is complete. Specific data are shown in Table 6. The withdrawal torque is basically insensitive to the thickness of the self-locking nut. Since the self-locking nut moves in parallel during withdrawal, the withdrawal torque provides thrust by causing the self-locking nut to cut off the external thread of the bolt.

[0133] Table 6

[0134]

[0135]

[0136] The internal thread of the self-locking nut can be formed by cutting or cold extrusion. The use of extrusion to achieve locking performance can improve thread accuracy, reduce roughness, increase thread surface hardness, and increase fatigue life. It is also conducive to shearing the external thread of the bolt.

Claims

1. A nut anti-loosening structure, comprising a bolt (1), a self-locking nut (3) and a part to be connected (5), characterized in that: The self-locking nut (3) is fixed on the bolt (1) via a self-locking area located in the middle of the bolt (1); A clamping member (2) is mounted on the bolt (1), and the clamping member (2) applies a clamping force to the connecting member (5); The clamping member (2) and the self-locking nut (3) form an integral structure, and the clamping member (2) and the self-locking nut (3) are assembled on the bolt (1) at the same time only by applying a torque to the self-locking nut (3); when the clamping force applied by the clamping member (2) to the connecting member (5) is sufficient, the connection between the inner and outer ring grooves between the clamping member (2) and the self-locking nut (3) is twisted off, so that the clamping member (2) and the self-locking nut (3) are separated, and the self-locking nut (3) continues to rotate to cut off the thread on the bolt (1) and fill its thread groove, so that the self-locking nut (3) is fixed on the bolt.

2. The nut anti-loosening structure according to claim 1, characterized in that: The self-locking area is formed by the thread on the bolt (1) being broken off and fractured, and the thread is filled in the thread groove of the self-locking nut (3) after being broken off and fractured.

3. A nut self-locking method using the nut anti-loosening structure according to claim 1, characterized in that: The self-locking nut is fixed on the bolt by destroying the screwing path of the self-locking nut on the bolt. The specific process is as follows: By controlling the thickness of the self-locking nut, during the assembly process of the self-locking nut and the bolt, the external thread on the bolt that matches the nut is destroyed while the internal thread of the nut is not destroyed by continuously applying torque to the self-locking nut.

4. The nut self-locking method according to claim 3, characterized in that: Before assembling the self-locking nuts and bolts, a standard nut is first used to apply a clamping force to the connection piece.

5. The method for preventing a nut from loosening according to claim 3, wherein: The thickness calculation process of the self-locking nut is: Normal stress in the bolt threaded shank: σrod = F / Arod; Shear force on a single thread: Fs = F / Z; Bolt thread shear stress: τ outer grain = 3 / 2Fs / A outer grain = 1.5F / ZA outer grain; Equivalent shear stress of bolt thread: , , Equivalent shear stress area of bolt thread , ; The relationship between the shear stress of the bolt thread and the normal stress of the bolt screw is: , , , , , Formula (1) is obtained: ； Then pass , Formula (2) is obtained: ； Further deduction can be made to obtain formula (3): ； Substituting formula (2) and formula (3) into formula (1), we get formula (4): ； In standard bolts, the relationship between pitch P and major diameter d of external thread is commonly used: 6P≤d≤9P, Substituting the above relationship into formula (4), we can obtain the minimum number of standard nut thread turns to ensure that the bolt thread is not damaged during the tightening process of the standard nut: When d=6P, Z=4, When d = 9P, Z = 6.6; Then the thickness H of the self-locking nut is: H self-locking<ZP; In the above formula: d1 is the thread minor diameter, H is the height of the original triangle, d3 is the basic minor diameter of the thread, d is the major diameter of the external thread, P is the pitch, Z is the number of engagement turns between the nut and the bolt, D is the major diameter of the internal thread, σ is the normal stress of the shank bolt screw, τ is the shear stress of the external thread bolt, A is the stress area of the shank bolt screw, A′ is the equivalent shear stress area of a single thread of the external thread bolt, F is the clamping force, Fs is the shear force applied to a single thread, and A is the stress area of a single external thread of the bolt.

6. The nut self-locking method according to claim 3, characterized in that: During the assembly process of the bolt and the self-locking nut, the torque gradually increases from zero and then suddenly drops to zero, and the self-locking nut completes self-locking.

7. The method for preventing a nut from loosening according to claim 4, wherein: When the self-locking nut is disassembled, the self-locking nut is withdrawn by disassembling the standard nut.

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