Hexagonal self-locking nut and its closing and coating processes

Abstract

This invention provides a hexagonal self-locking nut and its finishing and coating processes. The finishing process includes: solution heat treatment of the hexagonal self-locking nut; aging heat treatment of the hexagonal self-locking nut; and six-point finishing of the hexagonal self-locking nut, with a single-sided finishing amount of 0.10-0.20 mm, completing the finishing process. The six-point finishing involves first finishing three points on three non-adjacent sides of the hexagonal self-locking nut, and then finishing the remaining three non-adjacent sides with another three points. This finishing process, based on solution and aging treatments and a small-amount six-point finishing, can meet the locking stability requirements of the self-locking nut. This invention also provides a coating process based on the above finishing process, which can solve the problems of uneven internal thread coating and tooth root accumulation that occur when using molybdenum disulfide coatings on self-locking nuts, meeting the coating technology requirements for aerospace fasteners.

Description

Technical Field

[0001] This invention relates to a hexagonal self-locking nut and its closing and coating processes, belonging to the technical field of self-locking nut locking stability control. Background Technology

[0002] In aircraft component assembly, bolts and nuts are widely used for connection. However, in connection areas subjected to vibration and alternating loads, bolts and self-locking nuts are generally selected. The main factors affecting the locking performance of self-locking nuts include: the amount of tapering, the heat treatment process, and the internal thread coating process.

[0003] Previously, a three-point closing method was commonly used for hexagonal self-locking nuts. The current industry closing process involves: first, solution heat treatment of the nut, then closing the nut using a three-point closing fixture, with a single-sided closing amount of approximately 0.15-0.25 mm. The closed nut is then subjected to aging heat treatment to meet the standard requirement of 15 locking torques. This process has strict requirements on the dimensional accuracy of the closing amount; a slightly smaller closing amount will result in insufficient locking torque to meet the process design requirements. Furthermore, this heat treatment process has a long cycle and a long turnaround time, causing difficulties in production scheduling. The three-point closing method requires a large closing amount, resulting in significant plastic deformation of the nut. When the nut is closed after solution and aging heat treatment, metallographic testing reveals cracks at the threads.

[0004] Currently, the coating process for bolts is relatively mature, and the coated product meets the requirements of the HB6688-92 standard for thermosetting molybdenum disulfide dry film lubricants. However, there is currently no corresponding coating process for nuts. Nuts have an internal thread structure, requiring both uniform coating thickness on the outer surface and consistent coating thickness at the root and crest of the internal thread, which greatly increases the difficulty of the nut coating process. Using existing molybdenum disulfide coating processes to coat nuts has revealed problems such as accumulation at the root of the internal thread and uneven coating on both sides of the thread, failing to meet the requirements of the HB7595 standard for MJ threaded self-locking nuts with an operating temperature not exceeding 425℃. This results in unstable locking performance of the nuts, making the products unable to meet supply requirements and hindering the promotion and use of nuts. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the purpose of this invention is to provide a closing process for a hexagonal self-locking nut, which can meet the locking stability requirements of the self-locking nut with a smaller closing amount.

[0006] The present invention also aims to provide a coating process for hexagonal self-locking nuts, which can obtain a uniform coating on the internal threads and avoid the problem of tooth root accumulation.

[0007] To achieve the above objectives, the present invention provides a finishing process for a hexagonal self-locking nut, which includes the following steps:

[0008] The hexagonal self-locking nut is subjected to solution heat treatment at a temperature of 800-850℃ for 1-3 hours, followed by water cooling.

[0009] Then, the hexagonal self-locking nut is subjected to aging heat treatment at a temperature of 550-600℃ for 10-15 hours, followed by air cooling.

[0010] The hexagonal self-locking nut is closed at six points using a closing tool, with a single-sided closing amount of 0.10-0.20mm, thus completing the closing process of the hexagonal self-locking nut.

[0011] The six-point closing process involves first closing the three non-adjacent sides of the hexagonal self-locking nut at three points, and then closing the remaining three non-adjacent sides at three points.

[0012] In the above-mentioned finishing process of the hexagonal self-locking nut, preferably, the six-point finishing is performed as follows: three finishing fixtures distributed at 120° intervals are respectively aligned with three non-adjacent sides of the hexagonal self-locking nut, and then three-point finishing is performed. After completion, the three finishing fixtures are rotated by 60° (or the fixtures are fixed and the hexagonal self-locking nut is rotated by 60°) so that the three finishing fixtures are respectively aligned with the three non-adjacent sides that have not been finished, and then three-point finishing is performed.

[0013] In the above-mentioned finishing process of the hexagonal self-locking nut, preferably, the solution heat treatment temperature is 820℃±5℃, and the heat holding time is 2-2.5 hours.

[0014] In the above-mentioned finishing process of the hexagonal self-locking nut, preferably, the temperature of the aging heat treatment is 560℃±5℃, and the heat preservation time is 10-12 hours.

[0015] In the above-mentioned closing process of the hexagonal self-locking nut, preferably, the single-sided closing amount is 0.10-0.15mm.

[0016] In the above-mentioned finishing process of the hexagonal self-locking nut, preferably, the finishing part of the hexagonal self-locking nut is rectangular, the length L of the rectangle is 1.0-3.0mm, the width B is 0.5-2.0mm, and the area S of the finishing part is 0.5-5.0mm². 2 The distance H between the upper edge of the hexagonal self-locking nut and the closing point is 1.0-3.0mm.

[0017] In the above-mentioned finishing process of the hexagonal self-locking nut, preferably, the length L of the rectangle is 1.8-2.5mm and the width B is 0.8-1.6mm.

[0018] In the above-mentioned finishing process of the hexagonal self-locking nut, preferably, the area S of the finished area is 1.3-4.0 mm. 2 .

[0019] In the above-mentioned closing process of the hexagonal self-locking nut, preferably, the distance H between the upper edge of the hexagonal self-locking nut and the closing position is 1.5-2.5mm.

[0020] In the above-mentioned closing process of the hexagonal self-locking nut, preferably, the closing fixture used is a pin-shaped closing fixture used in conjunction with an automatic closing machine, wherein one end of the closing fixture is the closing contact end, and the other end is the mounting and fixing end. The end face of the closing contact end is provided with a rectangular protrusion for applying pressure to squeeze and close the nut, and the mounting and fixing end is cylindrical with a milled surface for bolt locking.

[0021] In the above-mentioned closing process of the hexagonal self-locking nut, preferably, the sharp edge of the protrusion of the closing tool is rounded to reduce stress concentration at the nut's stress point.

[0022] The sealing process provided by this invention utilizes a six-point sealing method, allowing for a smaller sealing amount and reducing nut deformation. This enables sealing to be performed directly after solution heat treatment and aging heat treatment, achieving the locking stability requirements of a self-locking nut. Without this six-point sealing method, a larger sealing amount is required, and cracks may appear in the nut during extrusion sealing after solution heat treatment and aging heat treatment.

[0023] The present invention also provides a coating process for a hexagonal self-locking nut, which includes the following steps:

[0024] The hexagonal self-locking nut, whose end has been closed by the closing process provided by the present invention, is subjected to pulse anodizing treatment, followed by dip coating, centrifugal drying, low-temperature curing, surface spraying, and high-temperature curing to complete the coating process.

[0025] The process of dip coating, centrifugal drying, and low-temperature curing is repeated 4-10 times.

[0026] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the process of dip coating, centrifugal drying and low temperature curing is repeated 5-7 times.

[0027] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the centrifugal drying is carried out by a planetary centrifugal dryer. During the centrifugal drying process, the planetary centrifugal dryer has a revolution speed of 700-900 rpm and a rotation speed of 300-500 rpm, and the centrifugal drying time is 6-12 minutes.

[0028] In the above-mentioned coating process of hexagonal self-locking nuts, preferably, the surface spraying refers to coating the outer surface of the nut using a spray gun, wherein the pump speed of the spray gun is 5-15g / min, the surface spraying temperature is 15-50℃, the surface spraying distance is 100-500mm, and the surface spraying time is 1-2 hours.

[0029] In the above-mentioned coating process of hexagonal self-locking nuts, preferably, the pumping speed of the spray gun is 8-10 g / min.

[0030] In the above-mentioned coating process for hexagonal self-locking nuts, preferably, the distance of the spray gun is 150-300mm.

[0031] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the surface spraying temperature is 10-25℃.

[0032] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the surface spraying time is 1.2-1.8 hours.

[0033] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the high-temperature curing temperature is 120-250℃ and the time is 1-10 hours.

[0034] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the high-temperature curing temperature is 120-180℃ and the time is 2-4 hours.

[0035] In the coating process of the aforementioned hexagonal self-locking nut, preferably, the current density of the pulse anodizing treatment is 2-3 A / dm. 3 The time is 25-50 minutes.

[0036] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the immersion coating time is 10-20 minutes.

[0037] In the coating process of the above-mentioned hexagonal self-locking nut, preferably, the low-temperature curing temperature is 65-120℃ and the time is 60-90 minutes.

[0038] The coating process provided by this invention can be used to coat the closed nut to obtain a uniform internal thread coating, avoiding the problem of coating accumulation at the root of the thread. This can prevent the thread and bolt thread pair from seizing due to the accumulation of the internal thread root of the nut during the locking force test. Once seizing occurs, the locking test will fail.

[0039] The present invention also provides a hexagonal self-locking nut, wherein the inner thread surface and the outer surface of the hexagonal self-locking nut have a coating layer, and the coating layer is formed by the coating process provided by the present invention;

[0040] The coating on the surface of the internal thread does not accumulate at the root of the thread.

[0041] In the above-mentioned hexagonal self-locking nut, preferably, the thickness of the coating layer is 5-20 μm.

[0042] This invention provides a process based on solution treatment and aging, along with a six-point tapering method with minimal tapering, which can meet the locking stability requirements of self-locking nuts. The coating process proposed in this invention for the internal threads of self-locking nuts solves the problems of uneven coating and tooth root accumulation that occur when using molybdenum disulfide coatings on self-locking nuts, thus meeting the technical requirements for molybdenum disulfide coatings in aerospace fasteners.

[0043] The technical solution of the present invention has the following beneficial effects:

[0044] 1. The closing process of this invention enables the nut to meet the 5-times locking performance requirement in the technical standard within a small closing range (0.10-0.15mm on one side). The closing process of the self-locking nut is relatively easy and suitable for mass production.

[0045] 2. By adopting the sealing process of the present invention, a solution treatment + sealing heat treatment system can be used first, and then the nut can be sealed. This process can shorten the processing cycle and reduce the production workload in the workshop. Alternatively, solution treatment + aging raw materials can be used directly to process the nut shape and tapping, and then the sealing can be performed, saving heat treatment steps and reducing production costs.

[0046] 3. The coating process of the present invention adopts centrifugal drying, which can avoid the accumulation of threads at the root of the nut's internal thread.

[0047] 4. The coating process of this invention adopts a repeated cycle of dip coating and centrifugal drying, which can make the coating on the internal thread and the outer surface more uniform, and the thickness is between 5-20μm to meet the standard requirements.

[0048] 5. The coating process of this invention is simple and suitable for mass production. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of the hexagonal self-locking nut provided in Example 1 after the end is closed. Detailed Implementation

[0050] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0051] Example 1

[0052] This embodiment provides a finishing process for a hexagonal self-locking nut, which includes:

[0053] After tapping, the MJ nut was placed in a horizontal vacuum continuous water quenching furnace for solution heat treatment. The heat treatment process was as follows: solution temperature 820℃, holding time 2 hours, and water cooling.

[0054] Then the nut is removed and placed in a vacuum aging furnace for aging heat treatment. The heat treatment regime is as follows: aging temperature 560℃, holding time 10 hours, and air cooling.

[0055] The heat-treated nut is then sent to an automatic closing machine for six-point closing (three-point closing is performed twice; during the second closing, the workpiece is rotated 60° before the second closing). A rectangular square-head ejector tool is selected, with the ejector protruding 16mm from the end face of the mounting keyway. The position of the conveyor shaft of the closing equipment is set to 41.3mm, and the mold shaft closing position is set to 7.2mm. The single-sided closing amount of the nut is 0.12mm. The equipment is started to close the nut, resulting in a self-locking nut with a closed end.

[0056] The hexagonal self-locking nut has a rectangular opening with a length L of 2.2 mm, a width B of 1.6 mm, and an area S of 3.52 mm². 2 The distance H between the upper edge of the hexagonal self-locking nut and the closing position is 0.8mm, specifically as follows: Figure 1 As shown.

[0057] This embodiment also provides a finishing process for a hexagonal self-locking nut, which includes the following steps:

[0058] The self-locking nut after sealing is subjected to pulse anodizing treatment with a current density of 2A / dm. 3 Pulse duration 35 minutes;

[0059] To ensure effective bonding between the molybdenum disulfide coating and the pulse layer, the self-locking nut after pulse anodizing is immersed in the prepared molybdenum disulfide coating (HD7352) for 4 hours. After immersion, the self-locking nut is placed in a planetary centrifugal dryer for drying. The planetary speed is 850 rpm and the rotation speed is 320 rpm for 6 minutes.

[0060] Then, it is cured at 100℃ for 90 minutes.

[0061] The process involves repeated cycles of dip coating, centrifugal drying, and low-temperature curing six times.

[0062] Then, a rolling coating was performed, with a spray gun distance of 250mm, a pump speed of 2g / min, a spraying temperature of 60℃, and a spraying time of 4 hours.

[0063] The product is then cured at a high temperature of 200°C for 6 hours, and the coated self-locking nut is then obtained after being removed from the oven.

[0064] The self-locking nuts were subjected to coating thickness and tightening torque tests. The coating thickness was between 7.2-13.8 μm. The maximum tightening torque after 5 tightening torque tests was 2.31 N·m, and the minimum loosening torque after 5 tightening torque tests was 0.47 N·m, meeting the technical standard requirements. The technical standard requirements are: coating thickness 5-20 μm, maximum tightening torque after 5 tightening torque tests 2.7 N·m, and minimum loosening torque after 5 tightening torque tests 0.27 N·m.

[0065] Example 2

[0066] The difference between this embodiment and embodiment 1 is that only the amount of the closing edge is changed, which is adjusted to 0.14mm. The spraying process is the same as in embodiment 1, except that the repeated cycles of dip coating + spin drying + low temperature curing are changed to 5 times, while other processes remain unchanged.

[0067] The coating thickness of the self-locking nut obtained in this embodiment is between 6.8 and 13.9 μm; the maximum locking torque after 5 cycles is 2.60 N·m and the minimum loosening torque after 5 cycles is 0.64 N·m, which meets the technical standard requirements.

[0068] Example 3

[0069] The difference between this embodiment and embodiment 1 is that only the low-temperature curing time after dip coating is adjusted to 60 minutes, and the spraying process is the same as in embodiment 1. However, the repeated cycles of dip coating + spin drying + low-temperature curing are changed to 7 times, while other processes remain unchanged.

[0070] The coating thickness of the self-locking nut obtained in this embodiment is between 7.2 and 13.4 μm; the maximum locking torque after 5 cycles is 2.21 N·m and the minimum loosening torque after 5 cycles is 0.48 N·m, which meets the technical standard requirements.

[0071] Moreover, the self-locking nut product of this embodiment has a large shrinkage range, and a shrinkage amount of 0.12-0.14mm on one side can meet the standard requirements, and the shrinkage process is relatively easy to process.

[0072] Comparative Example 1

[0073] This comparative example provides a finishing and coating process for a hexagonal self-locking nut, which includes the following steps:

[0074] After tapping, the MJ nut was placed in a horizontal vacuum continuous water quenching furnace for solution heat treatment. The heat treatment process was as follows: solution temperature 820℃, holding time 2 hours, and water cooling.

[0075] After solution treatment, the nut is sent to the automatic closing machine for closing. The three-point closing method is selected, with the top pin protruding 16mm from the end face of the mounting keyway. The position of the conveyor shaft of the closing equipment is set to 41.3mm, the mold shaft closing position is set to 6.7 / 6.6 / 6.5 / 6.3mm, and the closing amount of the nut on one side is 0.18 / 0.19 / 0.20 / 0.21mm. The equipment is started to close the nut.

[0076] Then the nut is removed and placed in a vacuum aging furnace for aging heat treatment. The heat treatment regime is as follows: aging temperature 560℃, holding time 10 hours, and air cooling.

[0077] Then, the nuts are coated with molybdenum disulfide, following the process described in Example 1, to obtain four finished self-locking nuts after spraying.

[0078] Five tightening torque tests were conducted on the four self-locking nuts. The maximum tightening torques in the five tests were 1.2 N·m, 1.6 N·m, and 2.3 N·m (failure). The minimum loosening torques in the five tests were 0.27 N·m, 0.30 N·m, and 0.52 N·m (failure). Only the nut with a 0.20 mm reduction in diameter met the standard requirements for tightening torque.

[0079] If the reduction amount is too small, the tightening torque will be insufficient; if the reduction amount is too large, the nut threads will crack, and the nut tightening test will fail. It is evident that this process has strict requirements on the reduction amount range, and the processing difficulty of the reduction process is relatively high.

[0080] Comparative Example 2

[0081] After performing solution treatment and aging heat treatment on the MJ nut according to the heat treatment regime of Example 1, a three-point closing method was selected, with a single-sided closing amount of 0.20 mm (other parameters are the same as in Example 1). The equipment was started to perform the closing process on the nut. The molybdenum disulfide coating process is the same as in Example 1.

[0082] Five tightening torque tests were conducted on the coated nuts. Aging was detected in the nuts during the fourth cycle. Fluorescent inspection of the sealed nuts revealed cracks in the internal threads.

[0083] Comparative Example 3

[0084] After the MJ nut underwent solution treatment and aging heat treatment according to the heat treatment regime of Example 1, a six-point closing design was selected. The length L of the rectangle at the closing point was 2 mm, the width B was 1.2 mm, and the area S of the closing point was 2.4 mm². 2 The closing amount is set to 0.12 / 0.13 / 0.14mm respectively, and other processes remain unchanged. The equipment is started to close the nuts. The molybdenum disulfide coating process is the same as in Example 1.

[0085] Five tightening torque tests were conducted on the coated nuts. The maximum tightening torques were 1.12 N·m, 1.34 N·m, and 1.53 N·m, respectively, and the minimum loosening torques were 0.15 N·m, 0.19 N·m, and 0.31 N·m, respectively. The data shows that only when a large reduction in opening (0.14 mm) is used can the tightening torque meet the standard requirements in five tests. When the compression area of ​​the closing fixture decreases, the deformation of the nut also decreases, and the tightening torque decreases accordingly. This demonstrates that the compression area of ​​the closing fixture is also a crucial factor in determining whether the tightening torque meets the standard.

[0086] Comparative Example 4

[0087] The difference between this comparative example and Example 1 is that only the low-temperature curing time after dip coating is adjusted to 30 minutes, and the spraying process is the same as in Example 1, except that the repeated cycles of dip coating + spin drying + low-temperature curing are changed to 3 times, while other processes remain unchanged.

[0088] The coating thickness of the self-locking nuts obtained in this comparative example is between 2.2 and 4.3 μm, and the coating on the inner thread of the finished nut shows a bottoming-out accumulation phenomenon.

[0089] After the nut is finished by the finishing process in Example 1, it is then dip-coated with molybdenum disulfide (once) and then rolled (refer to Example 1). The coating on the inner thread of the finished nut shows a bottoming-out accumulation phenomenon.

Claims

1. A process for closing a hexagonal self-locking nut, characterized in that, Includes the following steps: The hexagonal self-locking nut is subjected to solution heat treatment at a temperature of 820℃±5℃ for 2-2.5 hours, followed by water cooling. Then, the hexagonal self-locking nut is subjected to aging heat treatment at a temperature of 560℃±5℃ for 10-12 hours, followed by air cooling. After solution heat treatment and aging heat treatment, the hexagonal self-locking nut is directly closed at six points using a closing fixture, with a single-sided closing amount of 0.14-0.15 mm, thus completing the closing process of the hexagonal self-locking nut. in, The six-point closing is performed as follows: three closing fixtures spaced 120° apart are aligned with three non-adjacent sides of the hexagonal self-locking nut, and then the three-point closing is performed. After completion, the three closing fixtures are rotated 60° or the fixtures are fixed and the hexagonal self-locking nut is rotated 60° so that the three closing fixtures are aligned with the three non-adjacent sides that have not been closed, and then the three-point closing is performed. The hexagonal self-locking nut has a rectangular opening, with a length L of 1.8-2.5 mm, a width B of 0.8-1.6 mm, and an area S of 1.44-4.0 mm². 2 The distance H between the upper edge of the hexagonal self-locking nut and the closing point is 1.5-2.5 mm.

2. A coating process for hexagonal self-locking nuts, characterized in that, Includes the following steps: The hexagonal self-locking nut, which has been closed by the closing process of the hexagonal self-locking nut described in claim 1, is subjected to pulse anodizing treatment, and then dip coating, centrifugal drying, low-temperature curing, surface spraying, and high-temperature curing to complete the coating process. The process of dip coating, centrifugal drying, and low-temperature curing is repeated 5-7 times. The centrifugal drying is carried out using a planetary centrifugal dryer. During the centrifugal drying process, the planetary centrifugal dryer has a revolution speed of 700-900 rpm and a rotation speed of 300-500 rpm. The centrifugal drying time is 6-12 minutes. The temperature for low-temperature curing is 65-100℃; The surface spraying refers to coating the outer surface of the hexagonal self-locking nut with a spray gun, wherein the pumping speed of the spray gun is 5-15g / min, the surface spraying temperature is 15-50℃, the surface spraying distance is 100-500mm, and the surface spraying time is 1-2 hours. The high-temperature curing temperature is 120-250℃.

3. The coating process for hexagonal self-locking nuts according to claim 2, characterized in that, The pumping speed of the spray gun is 8-10 g / min.

4. The coating process for the hexagonal self-locking nut according to claim 2, characterized in that, The distance for surface spraying is 150-300mm.

5. The coating process for the hexagonal self-locking nut according to claim 2, characterized in that, The surface coating temperature is 10-25℃.

6. The coating process for the hexagonal self-locking nut according to claim 2, characterized in that, The high-temperature curing time is 1-10 hours.

7. The coating process for the hexagonal self-locking nut according to claim 6, characterized in that, The high-temperature curing temperature is 120-180℃, and the time is 2-4 hours.

8. The coating process for the hexagonal self-locking nut according to claim 2, characterized in that, The pulse anodizing treatment has a current density of 2-3 A / dm³ and a duration of 25-50 minutes.

9. The coating process for the hexagonal self-locking nut according to claim 2, characterized in that, The dipping time is 10-20 minutes.

10. The coating process for the hexagonal self-locking nut according to claim 2, characterized in that, The low-temperature curing time is 60-90 minutes.

11. A hexagonal self-locking nut, characterized in that, The hexagonal self-locking nut has a coating layer on its internal thread surface and external surface, and the coating layer is formed by the coating process described in any one of claims 2-10; The coating on the surface of the internal thread does not accumulate at the root of the thread.

12. The hexagonal self-locking nut according to claim 11, characterized in that, The thickness of the coating layer is 5-20 μm.

Images