A process optimization method for preventing abnormal fracture of double-strut clasps

Abstract

This invention discloses a process optimization method for preventing abnormal breakage of double-strand bolt retaining rings, belonging to the field of mechanical manufacturing technology. The method includes the following steps: a) optimizing the design of the retaining ring thickness tolerance and bushing recess depth tolerance; b) adjusting the base step height of the bushing tooling to 1.00-1.10 mm; c) inserting the bolt into the structural hole, performing symmetrical installation during the installation process, and using power tools or pneumatic tools for low-speed and medium-torque installation; d) applying dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing. This invention effectively avoids kinematic hardening caused by the Bagsinger effect by reducing the friction coefficient of the contact surface, thus effectively preventing abnormal breakage of the retaining ring during the reciprocating assembly and disassembly of double-strand bolts.

Description

Technical Field

[0001] This invention relates to the field of mechanical manufacturing technology, and in particular to a process optimization method for preventing abnormal breakage of double-strut bolt retaining rings. Background Technology

[0002] During production, it was discovered that the retaining rings of some double-line bolts on the caps were broken. The fracture modes were classified into four types: single-point crack, one-point, three-point, and four-point fracture, with the fracture locations all located in the four concave arc areas of the retaining ring.

[0003] The double-strand bolt is assembled from a slotted bolt, a retaining ring, and a shaped spring. The retaining ring is a sub-component of the double-strand bolt. Its design is similar to a washer. Structurally, it includes two inwardly protruding rectangular teeth, which are designed to slide freely along the bolt axis in the slotted area of ​​the bolt; and four outwardly concave arc areas, which are used to avoid the obstruction of the shaped spring when removing the retaining ring.

[0004] The working principle of the double-threaded bolt is as follows: First, the bolt thread is a double-ended thread, which enables quick installation and disassembly; second, the design of the retaining ring and the special-shaped spring can limit the displacement when the bolt is unscrewed, which can prevent the bolt from falling off the outlet cover during disassembly. That is, after disassembly, the double-threaded bolt can still be hung on the outlet cover for easy installation next time; third, since the bolt will not be removed from the outlet cover, it can prevent the bolt from being installed incorrectly during the next installation.

[0005] Double-strand bolts are typically used in conjunction with specialized bushings and floating nuts; this combination of double-strand bolts, bushings, and floating nuts is known as a double-strand bolt assembly. Double-strand bolt assemblies are generally installed on caps and frames.

[0006] The chamfered root of the inner surface of the retaining ring is prone to breakage under overload. The main reasons for this failure are:

[0007] 1. Inappropriate design tolerance

[0008] The bushing recess depth and retaining ring thickness tolerance are not properly distributed, and there are cases where the retaining ring thickness is greater than the bushing recess depth. In this case, after installation, the retaining ring is clamped in the structural interlayer and cannot rotate. When the bolts are installed or removed, it is subjected to torsional impact force, which causes the retaining ring to be sheared.

[0009] 2. The bushing installation tool is poorly designed.

[0010] According to the design drawings and physical inspection at the production site, the base steps are all 0.80-0.82 mm. This requirement will cause the bottom surface of the bushing countersunk hole to bulge and the recess depth to become shallower. This may exacerbate the situation where the retaining ring is clamped in the structure and cannot rotate, leading to the breakage of the retaining ring.

[0011] 3. Misalignment between the cap hole and the frame hole, and stress concentration caused by excessive speed of the installation tool, can lead to breakage of the retaining ring; forced assembly due to misalignment during double-bolt installation can also cause the retaining ring to break.

[0012] 4. Bauschinger effect of retaining ring material: In actual production, double-wire bolts will undergo repeated disassembly and assembly, which will cause the retaining ring to reciprocate within the bushing. Finite element analysis found that the shape of the retaining ring will undergo reciprocating tensile and compressive deformation during the reciprocating motion, which will lead to the kinematic hardening phenomenon under the Bauschinger effect of the material, and will also easily cause the retaining ring to break.

[0013] Existing technologies simply control the dimensional tolerances of the retaining ring and structure in an attempt to solve this problem, but in practice, recurring failures still occur from time to time, and the problem has not been fundamentally solved.

[0014] Chinese patent document CN118257773A, published on June 28, 2024, discloses a method for fixing a retaining ring connecting a compensating block fixing screw. The method is characterized by using a non-metallic bushing. The bushing is made of a non-metallic material. Before assembling the compensating block fixing screw, the bushing is fitted onto the outer circumference of the cylindrical section of the compensating block fixing screw. Then, the threaded section of the screw is screwed into the external engine body, and torque is applied. The compensating block fixing screw compensates for the radial gap between the cylindrical section of the compensating block fixing screw and the notch of the compensating block through the fit between the bushing and the notch of the compensating block.

[0015] The method for fixing the compensating block fixing screw using a retaining ring disclosed in this patent document can eliminate the radial gap between the compensating block fixing screw and the compensating block, achieving circumferential positioning of the compensating block. However, the kinematic hardening caused by the Bagsinger effect still exists, and it cannot effectively solve the problem of abnormal breakage of the retaining ring during the reciprocating assembly and disassembly process of the double-line bolt. Summary of the Invention

[0016] In order to overcome the defects of the prior art, the present invention provides a process optimization method for preventing abnormal breakage of double-wire bolt retaining rings. The present invention effectively avoids the kinematic hardening caused by the Bagsinger effect by reducing the friction coefficient of the contact surface, and can effectively prevent abnormal breakage of retaining rings during the reciprocating disassembly and assembly process of double-wire bolts.

[0017] This invention is achieved through the following technical solution:

[0018] A process optimization method for preventing abnormal fracture of double-strut bolt retaining rings, characterized by comprising the following steps:

[0019] a. Optimize the design tolerances for circlip thickness and bushing depth respectively;

[0020] b. Adjust the height of the base step of the bushing fixture to 1.00-1.10 mm;

[0021] c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use power tools or pneumatic tools to install at low speed and medium torque.

[0022] d. Apply dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing.

[0023] In step a, the thickness of the retaining ring is 0.76-0.82 mm.

[0024] In step a, the bushing recess depth is 0.85-0.9 mm.

[0025] In step b, the height of the base step is 1.05 mm.

[0026] In step c, symmetrical hole installation refers to tightening in a cross-tightening sequence or in steps according to the symmetrical axis sequence.

[0027] In step c, low speed refers to a speed of 150-200 rpm.

[0028] In step c, medium torque refers to a torque of 8-11 N·m.

[0029] In step d, the dry film lubrication treatment refers to the treatment using molybdenum disulfide lubricant or cetyl alcohol lubricant.

[0030] The thickness of the dry film lubrication treatment is 5-20 micrometers.

[0031] In step c, when the rotational speed is at the lower limit of the low rotational speed range, the installation is performed using the lower limit of the medium torque range; when the rotational speed is at the upper limit of the low rotational speed range, the installation is performed using the upper limit of the medium torque range.

[0032] The beneficial effects of this invention are mainly reflected in the following aspects:

[0033] 1. This invention: a) optimizes the design of the circlip thickness tolerance and bushing recess depth tolerance; b) adjusts the base step height of the bushing fixture to 1.00-1.10 mm; c) inserts the bolt into the structural hole, performs symmetrical installation of the hole positions during installation, and uses power tools or pneumatic tools for low-speed and medium-torque installation; d) applies dry film lubrication treatment to the inner surface of the circlip body and the countersunk hole side of the bushing. Compared with the prior art, this effectively avoids the kinematic hardening caused by the Bagsinger effect by reducing the friction coefficient of the contact surface, and can effectively prevent abnormal breakage of the circlip during the reciprocating disassembly and assembly process of the double-line bolt.

[0034] 2. In step a of this invention, the thickness of the retaining ring is 0.76-0.82 mm and the bushing recess depth is 0.85-0.9 mm. By using the retaining ring thickness and bushing recess depth within this specific range, a precise geometric coupling is formed, which can avoid overload and eliminate misalignment. The elastic deformation of the retaining ring and the rigid support of the bushing recess depth work together to reduce the peak contact stress by 35%, achieving effective fracture protection. The abnormal fracture rate of the double-line bolt retaining ring is reduced from 2.1% to 0.15%.

[0035] 3. In this invention, symmetrical hole installation refers to using a cross-tightening sequence or a step-by-step tightening sequence along the symmetrical axis to uniformize the stress transmission path of the multi-bolt structure, eliminate assembly off-center load, and achieve the core anti-breakage effect through dynamic balanced load distribution.

[0036] 4. In this invention, low speed refers to a speed of 150-200 rpm. Using this specific speed for installation can eliminate impact loads and improve the anti-breakage effect.

[0037] 5. In this invention, the film thickness of the dry film lubrication treatment is 5-20 micrometers. By using this specific film thickness, the coefficient of friction at the contact interface is reduced from 0.15 to 0.02-0.05, directly eliminating 75% of the fretting wear energy, isolating the electrochemical corrosion channel, and greatly reducing the risk of stress corrosion cracking.

[0038] 6. In step c of this invention, when the rotational speed is at the lower limit of the low rotational speed range, the installation is performed using the lower limit of the medium torque range; when the rotational speed is at the upper limit of the low rotational speed range, the installation is performed using the upper limit of the medium torque range. The low speed of 150 rpm is matched with a small torque, which can suppress the initial assembly impact and avoid brittle fracture of the retaining ring. The high speed of 200 rpm is matched with a large torque, which can overcome the dynamic friction attenuation of the system and eliminate fretting wear caused by loose tightening. Through the linkage control of low rotational speed and medium torque, the risk of breakage is greatly reduced.

[0039] 7. Compared with the prior art, the present invention eliminates assembly interference stress by precisely matching the tolerance design of the retaining ring and bushing through geometric adaptation; it blocks impact loads and off-center loads through the linkage control of low speed and medium torque and symmetrical installation of hole positions; it suppresses fretting wear through dry film lubrication treatment; and it locks the pre-compression amount with the tooling step height. This specific multi-dimensional collaborative control can systematically eliminate the risk of double-line bolt retaining ring breakage. Attached Figure Description

[0040] The present invention will now be further described in detail with reference to the accompanying drawings and specific embodiments:

[0041] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0042] Example 1

[0043] See Figure 1 A process optimization method for preventing abnormal fracture of double-strut clasps includes the following steps:

[0044] a. Optimize the design tolerances for circlip thickness and bushing depth respectively;

[0045] b. Adjust the height of the base step of the bushing fixture to 1.00 mm;

[0046] c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use power tools for low speed and medium torque installation.

[0047] d. Apply dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing.

[0048] This embodiment is the most basic implementation method. Compared with the prior art, by reducing the friction coefficient of the contact surface, it effectively avoids the kinematic hardening caused by the Bagsinger effect of the material, and can effectively avoid abnormal breakage of the retaining ring during the reciprocating disassembly and assembly process of the double-threaded bolt.

[0049] Example 2

[0050] See Figure 1 A process optimization method for preventing abnormal fracture of double-strut clasps includes the following steps:

[0051] a. Optimize the design tolerances for circlip thickness and bushing depth respectively;

[0052] b. Adjust the height of the base step of the bushing fixture to 1.10 mm;

[0053] c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use power tools for low speed and medium torque installation.

[0054] d. Apply dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing.

[0055] Preferably, in step a, the thickness of the retaining ring is 0.76 mm.

[0056] In step a, the bushing recess depth is 0.85 mm.

[0057] This embodiment is a preferred implementation method, which can avoid overload and eliminate misalignment. The elastic deformation of the retaining ring and the rigid support of the bushing recess work together to reduce the peak contact stress by 35%, achieving effective fracture protection. The abnormal fracture rate of the double-line bolt retaining ring is reduced from 2.1% to 0.15%.

[0058] Example 3

[0059] See Figure 1 A process optimization method for preventing abnormal fracture of double-strut clasps includes the following steps:

[0060] a. Optimize the design tolerances for circlip thickness and bushing depth respectively;

[0061] b. Adjust the height of the base step of the bushing fixture to 1.05 mm;

[0062] c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use power tools for low speed and medium torque installation.

[0063] d. Apply dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing.

[0064] In step a, the thickness of the retaining ring is 0.8 mm.

[0065] In step a, the bushing recess depth is 0.88 mm.

[0066] In step c, symmetrical hole installation refers to tightening in steps using a cross-tightening sequence.

[0067] In step c, low speed refers to a speed of 150 rpm.

[0068] In step c, a medium torque refers to a torque of 8 N·m.

[0069] This embodiment is another preferred implementation method, which makes the stress transmission path of the multi-bolt structure uniform, eliminates assembly off-center load, and achieves the core anti-breakage effect through dynamic balanced load distribution.

[0070] Example 4

[0071] See Figure 1 A process optimization method for preventing abnormal fracture of double-strut clasps includes the following steps:

[0072] a. Optimize the design tolerances for circlip thickness and bushing depth respectively;

[0073] b. Adjust the height of the base step of the bushing fixture to 1.10 mm;

[0074] c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use pneumatic tools for low-speed and medium-torque installation.

[0075] d. Apply dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing.

[0076] In step a, the thickness of the retaining ring is 0.82 mm.

[0077] In step a, the bushing recess depth is 0.9 mm.

[0078] In a further preferred embodiment, in step c, symmetrical hole installation refers to tightening in steps using a cross-tightening sequence.

[0079] In step c, low speed refers to a speed of 180 rpm.

[0080] In step c, medium torque refers to a torque of 10 N·m.

[0081] In step d, the dry film lubrication treatment refers to treatment using molybdenum disulfide lubricant.

[0082] The thickness of the dry film lubrication treatment is 5 micrometers.

[0083] This embodiment is another preferred implementation method, which reduces the friction coefficient of the contact interface from 0.15 to 0.02-0.05, directly eliminating 75% of the fretting wear energy, isolating the electrochemical corrosion channel, and greatly reducing the risk of stress corrosion cracking.

[0084] Example 5

[0085] See Figure 1 A process optimization method for preventing abnormal fracture of double-strut clasps includes the following steps:

[0086] a. Optimize the design tolerances for circlip thickness and bushing depth respectively;

[0087] b. Adjust the height of the base step of the bushing fixture to 1.10 mm;

[0088] c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use pneumatic tools for low-speed and medium-torque installation.

[0089] d. Apply dry film lubrication to the inner surface of the retaining ring body and the countersunk hole side of the bushing.

[0090] In step a, the thickness of the retaining ring is 0.82 mm.

[0091] In step a, the bushing recess depth is 0.9 mm.

[0092] In step c, symmetrical hole installation means tightening the holes step by step according to the symmetrical axis.

[0093] In step c, low speed refers to a speed of 200 rpm.

[0094] In step c, a medium torque refers to a torque of 11 N·m.

[0095] In step d, the dry film lubrication treatment refers to treatment using cetyl alcohol lubricant.

[0096] The thickness of the dry film lubrication treatment is 20 micrometers.

[0097] This embodiment represents the optimal implementation method. By precisely matching the tolerance design of the retaining ring and bushing through geometric adaptation, assembly interference stress is eliminated. Through the linkage control of low speed and medium torque and symmetrical installation of hole positions, impact loads and off-center loads are blocked. Dry film lubrication treatment suppresses fretting wear, and the pre-compression amount is locked by the tooling step height. This specific multi-dimensional collaborative control can systematically eliminate the risk of double-line bolt retaining ring breakage.

[0098] The basic principle of this invention is as follows:

[0099] Double-threaded bolt retaining ring breakage can be prevented by controlling assembly stress from multiple dimensions, including structural dimensions, assembly tools, installation processes, and material surface treatment.

[0100] First, optimize the geometric tolerance matching between the retaining ring and the bushing, specifically setting the retaining ring thickness to 0.76-0.82 mm and the bushing recess depth to 0.85-0.9 mm to eliminate initial assembly interference;

[0101] Secondly, the height of the base step of the bushing tooling is precisely controlled to 1.00-1.10 mm to limit the pre-compression; then, the dynamic fit of symmetrical hole installation combined with low speed of 150-200 rpm and medium torque of 8-11 N·m is used to avoid impact loads and off-center loads.

[0102] Finally, dry film lubrication is applied to the retaining ring-bulb contact interface. The dry film lubrication process follows either Hi-shear 292 "Molybdenum Disulfide Dry Film Lubrication for Fasteners" or Hi-shear 305 "Cetyl Alcohol Lubrication for Fasteners". The dry film lubrication treatment has a thickness of 5-20 micrometers, which can significantly reduce the coefficient of friction, thereby systematically suppressing stress concentration, fretting wear, and overload risks, achieving fracture protection.

Claims

1. A process optimization method for preventing abnormal fracture of double-strut bolt retaining rings, characterized in that, Includes the following steps: a. Optimize the design tolerances for circlip thickness and bushing depth respectively; b. Adjust the height of the base step of the bushing fixture to 1.00-1.10 mm; c. Insert the bolts into the structural holes, and install them symmetrically in the holes during the installation process. Use power tools or pneumatic tools to install at low speed and medium torque. d. Apply dry film lubrication to the inner surfaces of the retaining ring body and the countersunk side of the bushing; In step a, the thickness of the retaining ring is 0.76-0.82 mm; In step a, the bushing recess depth is 0.85-0.9 mm; In step c, low speed refers to a speed of 150-200 rpm; In step c, medium torque refers to a torque of 8-11 N·m; The thickness of the dry film lubrication treatment is 5-20 micrometers.

2. The process optimization method for preventing abnormal fracture of double-threaded bolt retaining rings according to claim 1, characterized in that: In step b, the height of the base step is 1.05 mm.

3. The process optimization method for preventing abnormal fracture of double-threaded bolt retaining rings according to claim 1, characterized in that: In step c, symmetrical hole installation refers to tightening in a cross-tightening sequence or in steps according to the symmetrical axis sequence.

4. The process optimization method for preventing abnormal fracture of double-threaded bolt retaining rings according to claim 1, characterized in that: In step d, the dry film lubrication treatment refers to the treatment using molybdenum disulfide lubricant or cetyl alcohol lubricant.

5. The process optimization method for preventing abnormal fracture of double-threaded bolt retaining rings according to claim 1, characterized in that: In step c, when the rotational speed is at the lower limit of the low rotational speed range, the installation is performed using the lower limit of the medium torque range; when the rotational speed is at the upper limit of the low rotational speed range, the installation is performed using the upper limit of the medium torque range.

Images