A nitriding fixture for internal toothed steel sheets and its application method

Abstract

This invention discloses a nitriding fixture and method for internally toothed steel sheets, belonging to the field of metal heat treatment tooling technology. It aims to solve problems such as easy attenuation of preload at high temperatures, rapid component wear, misalignment and reverse installation of steel sheets, and uneven nitriding quality in traditional nitriding fixtures. The fixture includes an upper pressure plate, a lower pressure plate, a connecting rod, and a locking nut. The upper end of the connecting rod is equipped with a detachable snap-fit ​​connector, and a replaceable silicon nitride ceramic bushing is provided at the snap-fit ​​position. A composite preload assembly consisting of an outer main load spring, an inner compensation spring, and a disc spring group is located within the limiting groove of the upper pressure plate. This invention employs a composite preload structure to ensure stable preload at high temperatures, the ceramic bushing enhances wear resistance and nitriding resistance, the positioning mandrel achieves precise circumferential positioning of the steel sheet, and the hollow structure improves the flow of nitriding gas. This fixture is easy to assemble and disassemble, has a long service life, effectively inhibits steel sheet warping and deformation, provides good nitriding quality, is adaptable to various specifications of internally toothed steel sheets, and is suitable for mass production.

Description

Technical Field

[0001] This invention relates to the field of metal heat treatment tooling technology, specifically to a nitriding fixture for internally toothed steel sheets and its method of use. Background Technology

[0002] Internal gear steel sheets are key precision components in transmission systems such as automotive gearboxes and industrial reducers. The hardness, wear resistance, and flatness of their tooth surfaces directly determine the service life and operational accuracy of the transmission system. To improve tooth surface strength and wear resistance, internal gear steel sheets typically undergo nitriding treatment. This process requires heating the workpiece to above 560℃ and holding it at that temperature for 3-5 hours. Because internal gear steel sheets are generally only 0.3-2mm thick, they are highly susceptible to warping and deformation at high temperatures, resulting in unusable flatness due to excessive flatness.

[0003] In existing technologies, simple clamps are commonly used for clamping, and some clamps may include a single set of helical springs to provide preload. However, the following technical problems remain difficult to solve in actual production: The preload stability is extremely poor: the elastic modulus of a single set of ordinary carbon steel springs decreases by more than 40% at a high temperature of 560℃, and irreversible creep is easily generated after long-term use, causing the clamp to gradually loosen during the nitriding process, and the warping deformation rate of the steel sheet is as high as 15% or more, which cannot meet the flatness requirement of ≤0.02mm for high-end products.

[0004] High maintenance costs for the fixture: The upper locking nut needs to be frequently disassembled, the mating threads are prone to wear and seizing in the high temperature nitriding environment, and the upper thread of the duct rod is an integral structure. After wear, the entire duct rod must be replaced. The cost of a single maintenance accounts for more than 30% of the total cost of the fixture.

[0005] Low clamping accuracy and prone to errors: There is no circumferential positioning structure, and the internal teeth are prone to misalignment when the steel sheets are stacked, resulting in local stress concentration and damage to the steel sheets during clamping; at the same time, there is no error prevention design, and steel sheets are prone to being installed backwards or missing, resulting in a scrap rate of about 5%.

[0006] To address the aforementioned issues, various improvement solutions have been attempted in the industry, such as increasing the number of springs, using high-temperature resistant spring materials, and manually placing spacers. However, none of these solutions have fundamentally resolved the main pain points, including preload decay, thread wear, and low clamping accuracy. Furthermore, they have introduced new problems such as complex operation and low production efficiency. Therefore, there is an urgent need to develop a special fixture for nitriding internally geared steel sheets that offers stable preload, high clamping accuracy, and long service life. Summary of the Invention

[0007] This invention provides a nitriding fixture for internal toothed steel sheets and a method for using it, which can solve the technical problems of existing conventional clamping fixtures such as preload decay, thread wear, low clamping accuracy, complex operation, and low production efficiency.

[0008] To achieve the above objectives, in a first aspect, the present invention provides the following technical solution: a nitriding fixture for internally toothed steel sheets, comprising an upper pressure plate and a lower pressure plate, wherein multiple guide rods are vertically inserted at the edge between the upper and lower pressure plates; a limiting groove is provided on the upper side of the upper pressure plate at a position corresponding to the guide rods; a gasket is provided on the upper side of the upper pressure plate at a position corresponding to the limiting groove; a detachable snap-fit ​​connector is connected to the upper end of each guide rod; and a sleeve is mounted on the upper side of the gasket outside the snap-fit ​​connector. The upper locking nut is connected by a side thread. A pre-tightening elastic component is installed within the limiting groove, with its upper end abutting against the upper locking nut and its lower end abutting against the lower end of the limiting groove. The lower end of the connecting rod is threadedly connected to a lower locking nut abutting against the lower side of the lower pressure plate. The upper and lower pressure plates are used to press and tighten the stacked internal toothed steel sheets. A detachable snap-fit ​​connector replaces the original integral threaded structure at the upper end of the connecting rod, separating the easily worn threaded part from the connecting rod. After the threads wear down, only the snap-fit ​​connector needs to be replaced, without scrapping the entire connecting rod. The integrated design of the limiting groove provides radial and axial dual limiting for the pre-tightening elastic component, preventing the spring from shifting under high-temperature vibration and ensuring that the pre-tightening force direction is always perpendicular to the pressure plate plane, avoiding lateral force that could cause steel sheet misalignment.

[0009] Preferably, the snap-fit ​​connector includes a snap-fit ​​end and a threaded post located on the upper side of the snap-fit ​​end. The lower side of the snap-fit ​​end is provided with a radially penetrating snap-fit ​​groove. The upper end of the connecting rod is provided with a snap-fit ​​head that matches the snap-fit ​​groove. The radial snap-fit ​​structure allows the snap-fit ​​connector to be installed and disassembled without rotating the connecting rod. It only needs to be pushed in or pulled out radially, which greatly improves the efficiency of changeover.

[0010] Preferably, a replaceable silicon nitride ceramic bushing is provided at the position where the outer side of the buckle head contacts the buckle groove. The silicon nitride ceramic has a hardness of HRA92 and its wear resistance is more than 50 times that of carbon steel. It can withstand more than 1,000 buckle-disconnect cycles without wear. The ceramic material does not react with nitrogen atoms and will not form a hard and brittle nitride layer under high-temperature nitriding environment, completely avoiding the problem of the buckle part seizing up. The bushing is installed with an interference fit. After wear, it only needs to be replaced by tapping, without replacing the buckle connector or the connecting rod.

[0011] Preferably, the preload elastic component includes an outer main load spring and an inner compensating spring arranged coaxially. The bottom of the limiting groove is provided with a disc spring group that supports the inner compensating spring and the outer main load spring. The outer main load spring provides 70% of the initial preload force, and the inner compensating spring is responsible for compensating for the high-temperature creep deformation of the outer spring. The combination of the two reduces the preload force attenuation rate from 40% to less than 5% at 580℃. At the same time, by utilizing the nonlinear stiffness characteristics of the disc spring, a stable preload force is provided within the range of total deformation ≤5mm, which offsets the small thermal deformation of the threaded pair and the steel sheet. The disc spring group is located at the bottom of the spring, which can evenly transmit the spring force to the upper pressure plate and avoid pressure plate deformation caused by local stress concentration.

[0012] Preferably, the outer main load spring is made of nickel-based high-temperature alloy, and the inner compensating spring is made of tungsten-nickel-copper alloy. The wire diameter of the outer main load spring is larger than that of the inner compensating spring. The nickel-based high-temperature alloy has an elastic modulus decrease of ≤30% at 580℃, high strength, and is suitable for bearing the main load; the tungsten-nickel-copper alloy has an elastic modulus decrease of ≤10% at 580℃, and is suitable as a compensating element. The difference in wire diameter makes the outer spring stiffer and able to bear the main load; the inner spring has lower stiffness and greater deformation. The deformation of the two springs is coordinated, avoiding mutual interference.

[0013] Preferably, both the upper and lower pressure plates are provided with hollowed-out slots in the middle. The hollowed-out slots in the middle greatly increase the flow area of ​​the nitriding gas, so that the inner tooth surface in the middle of the steel sheet can also fully contact the nitriding gas; this reduces the weight of the pressure plates, makes it easier for a single person to load and unload, and reduces labor intensity.

[0014] Preferably, a positioning mandrel is provided between the upper and lower pressure plates for detachable connection through a hollowed-out slot. The outer side of the positioning mandrel is provided with a toothed positioning groove that matches the inner teeth of the inner toothed steel sheet. The positioning mandrel can achieve precise circumferential positioning of the inner toothed steel sheet, avoiding pressure loss and uneven nitriding caused by misalignment of the inner teeth. Different specifications of inner toothed steel sheets can be adapted by changing the mandrel with different tooth shapes, without the need to replace the entire set of fixtures.

[0015] Preferably, the outer wall of the positioning mandrel is provided with axial scale markings, which can mark the number of internal toothed steel pieces when they are placed, eliminating the need for manual counting.

[0016] Preferably, the lower end of the positioning mandrel is provided with a mounting nut located on the lower side of the pressure plate to fix the positioning mandrel. The threaded connection structure is simple and can withstand the axial load of the stacked steel sheets without loosening after tightening.

[0017] Secondly, a method of using a nitriding fixture for internal toothed steel sheets as described in the first aspect includes the following steps: S1: Clamping preparation: Place the lower pressure plate horizontally, insert multiple rods vertically into the corresponding through holes on the edge of the lower pressure plate, and tighten the lower locking nut to fix the lower pressure plate and the lower end of the rods; pass the positioning mandrel from bottom to top through the hollow through groove in the middle of the lower pressure plate, and tighten it to the lower side of the lower pressure plate with the installation nut. S2: Snap-fit ​​installation: Align the snap-fit ​​groove of the snap-fit ​​connector with the snap-fit ​​head at the upper end of the rod, and push it in radially to complete the snap-fit, so that the snap-fit ​​connector and the upper end of the rod form a detachable axial connection; S3: Steel sheet stacking: Insert the internal toothed steel sheets into the positioning mandrel in sequence, so that the internal teeth of the internal toothed steel sheets mesh with the toothed positioning groove of the positioning mandrel. Confirm the stacking quantity through the scale on the positioning mandrel. S4: Pre-tightening installation: Insert the upper pressure plate into the multiple connecting rods, aligning the limiting groove of the upper pressure plate with the snap-fit ​​connector; place the disc spring group, inner compensation spring, and outer main load spring in each limiting groove in sequence, and then place the shim; use a torque wrench to tighten the upper locking nut to the rated pre-tightening force; S5: Nitriding treatment: Place the clamped fixture into the nitriding furnace, heat it to 560~580℃ and keep it at that temperature for 3~5 hours, and then introduce ammonia gas for gas nitriding treatment. S6: Disassembly and unloading: After cooling to room temperature after being removed from the furnace, loosen the upper locking nut, remove the washer and pre-tightening elastic component, remove the upper pressure plate in sequence, and remove the entire stack of internal toothed steel sheets from the positioning mandrel to complete the unloading.

[0018] Compared with the prior art, the technical solution of the present invention can achieve the following technical effects: Significantly improved preload stability: The three-stage composite preload structure, consisting of an outer main load spring, an inner compensation spring, and a disc spring, combined with the material properties of nickel-based high-temperature alloys and tungsten-nickel-copper alloys, significantly reduces the preload attenuation rate at 570℃, solving the problem of steel sheet warping caused by high-temperature loosening. The flatness of the steel sheet is controlled within 0.02mm, and the warping deformation rate is reduced to below 3%.

[0019] Significantly optimized clamp life and economy: The detachable snap-fit ​​connector replaces the integral thread of the traverse rod, and the silicon nitride ceramic wear-resistant bushing can prevent thread seizing and surface nitriding embrittlement, thereby increasing the average service life of the clamp and reducing maintenance costs.

[0020] The clamping accuracy and error prevention capabilities have been comprehensively upgraded: the toothed positioning mandrel achieves precise circumferential positioning of the internal teeth, integrates an anti-reverse placement boss and a counting scale ring, eliminates the problems of steel sheet misalignment and omission, and reduces the clamping scrap rate.

[0021] Nitriding quality and production efficiency are improved simultaneously: the hollowed-out through groove in the middle of the pressure plate greatly improves the flow of nitriding gas, and the difference in nitriding layer thickness between the tooth root and tooth tip is ≤0.01mm; the radial quick-release buckle shortens the single disassembly and assembly time, improves the clamping efficiency of a single furnace, and the modular mandrel design can be adapted to various specifications of steel sheets, reducing the cost of fixture inventory. Attached Figure Description

[0022] Figure 1 This is a front sectional view of the present invention; Figure 2 For the present invention Figure 1 Enlarged structural diagram at point I; Figure 3 This is a schematic diagram illustrating the fit between the positioning mandrel and the internal toothed steel sheet of the present invention. Figure 4 This is a flowchart illustrating the usage method of the present invention.

[0023] Figure label: 1. Upper pressure plate; 2. Lower pressure plate; 3. String rod; 4. Lower locking nut; 5. Mounting nut; 6. Positioning mandrel; 7. Upper locking nut; 8. Washer; 9. Snap-fit ​​connector; 91. Snap-fit ​​end; 92. Threaded post; 93. Snap-fit ​​groove; 10. Silicon nitride ceramic bushing; 11. Limiting groove; 12. Disc spring assembly; 14. Outer main load spring; 15. Inner compensation spring; 16. Hollow through groove; 31. Snap-fit ​​head; 61. Toothed positioning groove; A. Internal toothed steel plate. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0025] like Figure 1-4As shown, to solve the technical problems of existing conventional clamping fixtures, such as preload decay, thread wear, low clamping accuracy, complex operation, and low production efficiency, this invention provides the following technical solution: a nitriding fixture for internal toothed steel sheets, including an upper pressure plate 1 and a lower pressure plate 2, wherein multiple guide rods 3 are vertically inserted at the edge between the upper pressure plate 1 and the lower pressure plate 2, a limiting groove 11 is provided on the upper side of the upper pressure plate 1 at a position corresponding to the guide rods 3, a gasket 8 is provided on the upper side of the upper pressure plate 1 at a position corresponding to the limiting groove 11, and a detachable snap-fit ​​connector 9 is connected to the upper end of the guide rods 3. A locking nut 7, threaded onto the outside of the snap-fit ​​connector 9, is installed on the upper side of the gasket 8. A pre-tightening elastic component, with its upper end abutting against the locking nut 7 and its lower end abutting against the lower end of the limiting groove 11, is provided in the limiting groove 11. A lower locking nut 4, abutting against the lower side of the lower pressure plate 2, is threaded onto the lower end of the connecting rod 3. The upper pressure plate 1 and the lower pressure plate 2 are used to press and tighten the stacked internal toothed steel sheet A. The detachable snap-fit ​​connector 9 replaces the original integral threaded structure at the upper end of the connecting rod, separating the easily worn threaded part from the connecting rod. After the thread wears out, only the snap-fit ​​connector needs to be replaced, without scrapping the entire connecting rod. The integrated design of the limiting groove provides radial and axial dual limiting for the pre-tightening elastic component, preventing the spring from shifting under high-temperature vibration, ensuring that the pre-tightening force direction is always perpendicular to the pressure plate plane, and avoiding the generation of lateral force that could cause the steel sheet to misalign.

[0026] In this embodiment, the snap-fit ​​connector 9 includes a snap-fit ​​end 91 and a threaded post 92 located on the upper side of the snap-fit ​​end 91. A radially penetrating snap-fit ​​groove 93 is provided on the lower side of the snap-fit ​​end 91. The upper end of the connecting rod 3 is provided with a snap-fit ​​head 31 that matches the snap-fit ​​groove 93. The radial snap-fit ​​structure allows the snap-fit ​​connector 9 to be installed and disassembled without rotating the connecting rod, only by pushing it in or pulling it out radially, which greatly improves the efficiency of changing the type.

[0027] In this embodiment, a replaceable silicon nitride ceramic bushing 10 is provided at the position where the outer side of the buckle head 31 contacts the buckle groove 93. The silicon nitride ceramic has a hardness of HRA92 and its wear resistance is more than 50 times that of carbon steel. It can withstand more than 1,000 buckle disassembly cycles without wear. The ceramic material does not react with nitrogen atoms and will not form a hard and brittle nitride layer under high temperature nitriding environment, thus completely avoiding the problem of the buckle part seizing. The bushing is installed with an interference fit. After wear, it only needs to be replaced by tapping, without replacing the buckle connector or the connecting rod.

[0028] In this embodiment, the preload elastic component includes an outer main load spring 14 and an inner compensating spring 15 arranged coaxially. The bottom of the limiting groove 11 is provided with a disc spring group 12 that supports the inner compensating spring 15 and the outer main load spring 14. The outer main load spring provides 70% of the initial preload force, and the inner compensating spring is responsible for compensating for the high-temperature creep deformation of the outer spring. The combination of the two reduces the preload force attenuation rate from 40% to less than 5% at 580℃. At the same time, by utilizing the nonlinear stiffness characteristics of the disc spring, a stable preload force is provided within the range of total deformation ≤5mm, which counteracts the small thermal deformation of the threaded pair and the steel sheet. The disc spring group is located at the bottom of the spring, which can evenly transmit the spring force to the upper pressure plate and avoid pressure plate deformation caused by local stress concentration.

[0029] In this embodiment, the outer main load spring 14 is made of nickel-based high-temperature alloy, and the inner compensation spring 15 is made of tungsten-nickel-copper alloy. The wire diameter of the outer main load spring 14 is larger than that of the inner compensation spring 15. The nickel-based high-temperature alloy has an elastic modulus decrease of ≤30% at 580℃, high strength, and is suitable for bearing the main load; the tungsten-nickel-copper alloy has an elastic modulus decrease of ≤10% at 580℃, and is suitable as a compensation element. The difference in wire diameter makes the outer spring stiffer and able to bear the main load; the inner spring has lower stiffness and greater deformation. The deformation of the two is coordinated, avoiding mutual interference.

[0030] In this embodiment, both the upper pressure plate 1 and the lower pressure plate 2 are provided with hollowed-out through grooves 16 in the middle. The hollowed-out through grooves in the middle greatly increase the flow area of ​​the nitriding gas, so that the inner tooth surface in the middle of the steel sheet can also fully contact the nitriding gas; thus reducing the weight of the pressure plate, making it easier for a single person to load and unload, and reducing labor intensity.

[0031] In this embodiment, a positioning mandrel 6 is provided between the upper pressure plate 1 and the lower pressure plate 2, which can be detachably connected through a hollow slot 16. The outer side of the positioning mandrel 6 is provided with a tooth-shaped positioning groove 61 that matches the inner teeth of the inner tooth steel piece A. The positioning mandrel 6 can achieve precise circumferential positioning of the inner tooth steel piece A, avoiding pressure loss and uneven nitriding caused by misalignment of the inner teeth. Different sizes of inner tooth steel pieces can be adapted by changing the mandrel with different tooth shapes, without the need to change the entire set of fixtures. At the same time, the outer wall of the positioning mandrel 6 is provided with axial scale markings, which can mark the number of inner tooth steel pieces A when they are placed, eliminating the need for manual counting.

[0032] In this embodiment, the lower end of the positioning mandrel 6 is provided with a mounting nut 5 located on the lower side of the pressure plate 2 to fix the positioning mandrel 6. The threaded connection structure is simple and can withstand the axial load of the stacked steel sheets without loosening after tightening.

[0033] As a specific embodiment of the present invention: The internal gear steel sheet nitriding fixture disclosed in this embodiment is mainly used for the mass nitriding treatment of automotive clutch internal gear steel sheets A with a thickness of 0.5mm, an outer diameter of φ200mm, an inner diameter of φ80mm, a module of 2mm, and 36 teeth. The fixture adopts a modular design and mainly consists of four parts: a clamping mechanism, a preload compensation mechanism, a quick assembly / disassembly mechanism, and a positioning and error prevention mechanism.

[0034] The clamping mechanism includes an upper pressure plate 1, a lower pressure plate 2, four connecting rods 3, and a lower locking nut 4. Both the upper pressure plate 1 and the lower pressure plate 2 are circular steel plates, 20mm thick, made of 40Cr alloy steel. The outer surface and sides are coated with a 100μm thick aluminum nitride ceramic coating. The working surface in contact with the steel plates is not coated to ensure sufficient clamping friction. Both the upper pressure plate 1 and the lower pressure plate 2 have a circular hollow slot 16 with a diameter of 80mm in the center, and four connecting rod through holes with a diameter of 12mm are evenly distributed along the edges. The center of each through hole is located on a circumference with a diameter of 180mm. A limiting groove 11 is coaxially machined on the upper side of the upper pressure plate 1 with each connecting rod through hole. The limiting groove 11 has a diameter of 50mm, a depth of 45mm, and a coaxiality tolerance ≤0.02mm.

[0035] The connecting rod 3 is a cylindrical rod with a diameter of 12mm and a length of 350mm. It is made of 40Cr alloy steel and its surface is coated with an aluminum nitride ceramic coating. The lower end of the connecting rod 3 is machined with an M12×1.5 external thread, and the upper end is equipped with a cylindrical snap-fit ​​head 31 with a diameter of 10mm and a length of 20mm. The connecting rod 3 is vertically inserted into the connecting rod through hole of the lower pressure plate 2, and the lower end is tightened and fixed to the lower side of the lower pressure plate 2 by an M12 lower locking nut 4 with a tightening torque of 40N·m.

[0036] The quick-release mechanism includes four snap-fit ​​connectors 9 and a silicon nitride ceramic bushing 10. The snap-fit ​​connectors 9 are integrally machined from 40Cr alloy steel and include a snap-fit ​​end 91 and a threaded post 92. The snap-fit ​​end 91 is a cuboid with a thickness of 15mm and a radially penetrating snap-fit ​​groove 93 on its lower side. The snap-fit ​​groove 93 is T-shaped, 10mm wide, and 20mm deep. A 1mm thick silicon nitride ceramic bushing 10 is press-fitted into the snap-fit ​​groove 93 with an interference fit of 0.03mm. The threaded post 92 is located above the snap-fit ​​end 91, and has an M20×1.5 fine thread, a length of 30mm, and a thread accuracy of 6H. The snap-fit ​​connectors 9 radially snap into the snap-fit ​​head 31 at the upper end of the connecting rod 3 through the snap-fit ​​groove 93, achieving a detachable axial connection with an axial load capacity ≥25kN.

[0037] The preload compensation mechanism includes a preload elastic component, a washer 8, and an upper locking nut 7. The preload elastic component is installed in the limiting groove 11 of the upper pressure plate 1 and is composed of a disc spring assembly 12, an inner compensation spring 15, and an outer main load spring 14 nested coaxially. The disc spring assembly 12 is composed of 2-3 φ40 / φ20×1mm GH4169 disc springs stacked together and placed at the bottom of the limiting groove 11. The inner compensation spring 15 is made of tungsten-nickel-copper alloy W90Ni6Cu4, with a wire diameter of 3mm, a mean diameter of 28mm, 12 effective coils, and a free height of 75mm, and is coaxially placed above the disc spring assembly 12. The outer main load spring 14 is made of nickel-based high-temperature alloy GH4169, with a wire diameter of 6mm, a mean diameter of 40mm, 8 effective coils, and a free height of 80mm, and is coaxially sleeved on the outside of the inner compensation spring 15. All spring surfaces are coated with a 50μm thick silicon nitride ceramic coating to prevent nitriding embrittlement.

[0038] The washer 8 is a round steel washer placed above the pre-tightening elastic component. The upper locking nut 7 is a hexagonal nut made of 40Cr alloy steel with an aluminum nitride ceramic coating on the surface. It is threaded onto the threaded post 92 of the snap-fit ​​connector 9, and its lower end abuts against the washer 8.

[0039] The positioning and error-proofing mechanism includes a toothed positioning mandrel 6 and a mounting nut 5. The toothed positioning mandrel 6 passes through the hollowed-out slots 16 of the upper pressure plate 1 and the lower pressure plate 2, and has an external thread machined at its lower end. It is tightened and fixed to the lower side of the lower pressure plate 2 by the mounting nut 5, with a tightening torque of 30 N·m. The outer side of the positioning mandrel 6 has a toothed positioning groove 61 that is perfectly matched with the internal teeth of the internal toothed steel plate A. The groove has a module of 2 mm and 36 teeth, and adopts an H7 / g6 clearance fit with the internal teeth, with a circumferential positioning accuracy of ≤0.01 mm.

[0040] The toothed working surface of the positioning mandrel 6 is not coated, while the remaining surfaces are coated with a 100μm thick aluminum nitride ceramic coating. The outer circular surface of the mandrel is etched with graduated rings at 0.5mm intervals, with a number marking every 10 pieces.

[0041] An embodiment of the present invention also provides a method for using the nitriding fixture for the above-mentioned internal toothed steel sheet, comprising the following steps: S1: Clamping preparation: Place the lower pressure plate 2 horizontally, insert multiple rods 3 vertically into the corresponding through holes on the edge of the lower pressure plate 2, and tighten the lower locking nut 4 to fix the lower pressure plate 2 and the lower end of the rods 3; pass the positioning mandrel 6 from bottom to top through the hollow through groove 16 in the middle of the lower pressure plate 2, and tighten it to the lower side of the lower pressure plate 2 by tightening the mounting nut 5. S2: Snap-fit ​​installation: Align the snap-fit ​​groove 93 of the snap-fit ​​connector 9 with the snap-fit ​​head 31 at the upper end of the rod 3, and push it in radially to complete the snap-fit, so that the snap-fit ​​connector 9 and the upper end of the rod 3 form a detachable axial connection. S3: Steel sheet stacking: Insert the inner toothed steel sheet A into the positioning mandrel 6 in sequence, so that the inner teeth of the inner toothed steel sheet A engage with the toothed positioning groove 61 of the positioning mandrel 6, and confirm the stacking quantity through the scale on the positioning mandrel 6. S4: Pre-tightening installation: Insert the upper pressure plate 1 into the multiple connecting rods 3, so that the limiting groove 11 of the upper pressure plate 1 is aligned with the snap-fit ​​connector 9; place the disc spring group 12, the inner compensation spring 15, and the outer main load spring 14 in each limiting groove 11 in sequence, and then place the shim 8; use a torque wrench to tighten the upper locking nut 7 to the rated pre-tightening force. S5: Nitriding treatment: Place the clamped fixture into the nitriding furnace, heat it to 560~580℃ and keep it at that temperature for 3~5 hours, and then introduce ammonia gas for gas nitriding treatment. S6: Disassembly and unloading: After cooling to room temperature after being removed from the furnace, loosen the upper locking nut 7 in sequence, remove the washer 8 and the pre-tightening elastic component, remove the upper pressure plate 1, and remove the entire stack of internal toothed steel sheets A from the positioning mandrel 6 to complete the unloading.

[0042] As a complete implementation of the above usage method: Pre-implementation preparation: (1) Inspect the appearance of all fixture parts: confirm that there are no scratches, deformations and nitriding layer accumulation on the working surfaces of the upper pressure plate 1 and the lower pressure plate 2; no bending deformation of the connecting rod 3; no cracks or loosening of the silicon nitride ceramic bushing 10 in the snap groove 93 of the snap fastener 9; and no permanent deformation or breakage of the pre-tightening elastic component.

[0043] (2) Clean all mating surfaces: Wipe the buckle head 31 of the rod 3, the inner surface of the silicon nitride ceramic bushing 10 of the buckle connector 9, the working surface of the upper and lower pressure plates, and the toothed positioning groove 61 of the toothed positioning mandrel 6 with anhydrous ethanol to remove oil and oxide scale.

[0044] (3) Nitriding Furnace Preparation: Clean the nitriding furnace chamber and furnace tank, removing iron nitride deposits from the furnace walls. Purge the furnace chamber with nitrogen for 10 minutes to remove air and prevent workpiece oxidation. Set the nitriding process parameters: heating rate 10℃ / min, nitriding temperature 570℃±5℃, holding time 4 hours, ammonia flow rate 0.8m³ / min. 3 / h, furnace pressure 500~800Pa.

[0045] Fixture assembly steps: The lower pressure plate is fixed to the connecting rod: Place the lower pressure plate 2 horizontally on the dedicated workbench with the working surface facing upwards, ensuring the lower pressure plate is placed stably with a flatness error ≤0.02mm / m. Insert the four connecting rods 3 into the four φ12mm through holes on the edge of the lower pressure plate 2 from bottom to top, with the threaded lower end of the connecting rods extending 15mm beyond the lower side of the lower pressure plate. Using a 40N·m torque wrench, tighten the four lower locking nuts 4 in a diagonal sequence to firmly fix the lower pressure plate 2 and the connecting rods 3. After tightening, use a right-angle ruler to check the verticality of the connecting rods; the verticality tolerance ≤0.05mm / 300mm.

[0046] Toothed positioning mandrel installation: Insert the toothed positioning mandrel 6 of the corresponding specification through the hollowed-out through slot 16 in the middle of the lower pressure plate 2 from bottom to top, with the threaded lower end of the mandrel extending 12mm beyond the lower pressure plate. Screw in the M16 mounting nut 5 at the lower end of the mandrel and tighten it with a 30 N·m torque wrench to ensure that the positioning mandrel 6 is vertically fixed, and the perpendicularity tolerance between the mandrel axis and the plane of the lower pressure plate is ≤0.03mm / 300mm. Confirm that the scale ring is clearly readable, with a 0.5mm interval, and one number is marked for every 10 pieces.

[0047] Clip-on connector installation: Take four pre-installed silicon nitride ceramic bushings 10 and check whether the bushing interference fit is firm and not loose. Align the radial through-groove 93 of each snap-fit ​​connector 9 with the cylindrical snap head 31 at the upper end of the corresponding rod 3, and push it in smoothly in the horizontal direction until the snap head is completely inserted into the bottom of the snap groove.

[0048] Pull the buckle connector upwards by hand to confirm that there is no axial looseness and that it is securely fastened; if it is loose, replace the ceramic bushing and reinstall.

[0049] Internal toothed steel sheet stacking steps: Take the internal tooth steel sheet A that has been pretreated by degreasing and rust removal, hold the edge of the steel sheet, align the internal teeth with the toothed positioning groove 61 of the toothed positioning mandrel 6, and slowly slide it down.

[0050] If the steel sheet cannot be smoothly inserted, it indicates that the steel sheet is reversed or there are burrs on the internal teeth. In this case, the anti-reverse protrusion will press against the end face of the steel sheet, making the steel sheet 2mm higher than the end face of the mandrel. Immediately flip the steel sheet and reinstall it. If it is a burr problem, use fine sandpaper to polish the burrs before reinstalling.

[0051] The steel sheets are stacked sequentially, with 10 sheets stacked at a time. The scale ring on the mandrel is checked once to ensure the accuracy of the stacking quantity. In this embodiment, the number of sheets clamped in a single furnace is 100, and the total height after stacking is 50mm.

[0052] After stacking, gently rotate the top layer of steel sheet by hand to confirm that all steel sheets are engaged with the mandrel teeth and there is no circumferential looseness.

[0053] Installation and adjustment of preload mechanism: Insert the upper pressure plate 1 horizontally into the four connecting rods 3, aligning the limiting groove 11 of the upper pressure plate with the snap fastener 9 above, and slowly lower the upper pressure plate so that it is in close contact with the uppermost steel sheet.

[0054] Pre-tightening elastic components are sequentially placed in each limiting groove 11: Step 1: Place in the three stacked disc springs 12, with the concave side of the disc springs facing up; Step 2: Insert the inner compensation spring 15 of tungsten-nickel-copper alloy, ensuring that the spring is placed coaxially in the center of the disc spring assembly; Step 3: Insert the nickel-based high-temperature alloy outer main load spring 14, which is coaxially sleeved on the outside of the inner compensation spring.

[0055] A steel shim 8 is placed above each pre-tightened elastic component, with the shim plane in close contact with the spring end face.

[0056] Screw the upper locking nut 7 into the threaded post 92 of the snap-fit ​​connector 9, and pre-tighten by hand until the nut contacts the washer. Using a 50 N·m torque wrench, tighten the four upper locking nuts evenly in three diagonal stages: First tightening: Tighten to 25 N·m, corresponding to a preload of 10 kN; Second time: Tighten to 40 N·m, corresponding to a preload of 16 kN; Third time: Tighten to 50 N·m, corresponding to a rated preload of 20 kN.

[0057] After pre-tightening, check whether the compression of the four springs is consistent, and the compression is 10mm±0.5mm. If the difference exceeds 1mm, readjust the tightening torque of the corresponding nut.

[0058] Nitriding furnace in-process treatment: Using a crane, smoothly lift the clamped fixture into the nitriding furnace tank and place it on the furnace bottom support, ensuring the fixture is vertical and not tilted. Close the furnace lid, seal the furnace tank, and purge with nitrogen again for 5 minutes. Start the heating program, raising the temperature to 570°C at a rate of 10°C / min, maintaining an ammonia flow rate of 0.5 m³ / min during the heating process. 3 / h.

[0059] When the furnace temperature reaches 570℃, adjust the ammonia flow rate to 0.8m³. 3 Start the heat preservation timer at / h, and maintain the heat preservation for 4 hours; during the heat preservation process, record the furnace temperature, ammonia flow rate and furnace pressure every 30 minutes to ensure that the parameters are stable within the set range.

[0060] During nitriding, the gradient stiffness composite preload mechanism automatically compensates for high-temperature deformation: the outer main load spring provides the main preload, the inner compensating spring compensates for the high-temperature creep of the outer spring, and the disc spring assembly counteracts the minor thermal deformation of the threaded joint and steel sheet, keeping the total preload attenuation rate below 5%. Cooling and unloading steps: After the heat preservation is completed, stop heating, close the ammonia valve, and introduce nitrogen for forced cooling. The cooling rate should be controlled within 5℃ / min to prevent the steel sheets from deforming due to excessive cooling. When the furnace temperature drops below 200℃, open the furnace lid and continue to cool naturally to room temperature (≤40℃). Use a crane to lift the fixture out of the furnace and place it on the workbench. Using a 50N·m torque wrench, loosen the four upper locking nuts 7 in a diagonal sequence, and remove the washer 8, outer main load spring 14, inner compensation spring 15, and disc spring assembly 12 in sequence. Lift the upper pressure plate 1 vertically upwards and place it aside. Hold the edges of the entire stack of steel sheets with both hands and remove them vertically upwards from the toothed positioning mandrel 6, placing them on a special material rack. If the steel sheet fits tightly with the mandrel, you can gently tap the bottom edge of the steel sheet with a copper rod, but be careful not to tap the toothed surface.

[0061] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0062] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0063] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0064] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A nitriding fixture for internally toothed steel sheets, characterized in that, Includes an upper pressure plate (1) and a lower pressure plate (2). Multiple rods (3) are vertically inserted through the edge between the upper pressure plate (1) and the lower pressure plate (2). A limiting groove (11) is provided on the upper side of the upper pressure plate (1) corresponding to the rods (3). A gasket (8) is provided on the upper side of the upper pressure plate (1) corresponding to the limiting groove (11). A detachable snap-fit ​​connector (9) is connected to the upper end of each rod (3). The gasket (8)... 8) is fitted with an upper locking nut (7) threaded on the outside of the snap fastener (9). The limiting groove (11) is provided with a pre-tightening elastic component whose upper end abuts against the upper locking nut (7) and whose lower end abuts against the lower end of the limiting groove (11). The lower end of the string rod (3) is threaded with a lower locking nut (4) abutting against the lower side of the lower pressure plate (2). The upper pressure plate (1) and the lower pressure plate (2) are used to press the stacked internal toothed steel sheet (A).

2. The nitriding fixture for internal toothed steel sheets according to claim 1, characterized in that: The snap-fit ​​connector (9) includes a snap-fit ​​end (91) and a threaded post (92) located on the upper side of the snap-fit ​​end (91). A radially penetrating snap-fit ​​groove (93) is provided on the lower side of the snap-fit ​​end (91). A snap-fit ​​head (31) matching the snap-fit ​​groove (93) is provided on the upper end of the rod (3).

3. The nitriding fixture for internal toothed steel sheets according to claim 2, characterized in that: A replaceable silicon nitride ceramic bushing (10) is provided at the position where the outer side of the buckle head (31) contacts the buckle groove (93).

4. The nitriding fixture for internal toothed steel sheets according to claim 2, characterized in that: The pre-tightening elastic component includes an outer main load spring (14) and an inner compensation spring (15) arranged coaxially. The bottom of the limiting groove (11) is provided with a disc spring group (12) that supports the inner compensation spring (15) and the outer main load spring (14).

5. The nitriding fixture for internal toothed steel sheets according to claim 4, characterized in that: The outer main load spring (14) is made of nickel-based high-temperature alloy material, and the inner compensation spring (15) is made of tungsten-nickel-copper alloy material. The wire diameter of the outer main load spring (14) is larger than that of the inner compensation spring (15).

6. The nitriding fixture for internal toothed steel sheets according to claim 4, characterized in that: Both the upper pressure plate (1) and the lower pressure plate (2) are provided with hollow through grooves (16) in the middle.

7. The nitriding fixture for internal toothed steel sheets according to claim 6, characterized in that: A positioning mandrel (6) is provided between the upper pressure plate (1) and the lower pressure plate (2) and can be detachably connected through the hollow slot (16). The outer side of the positioning mandrel (6) is provided with a toothed positioning groove (61) that matches the inner teeth of the inner toothed steel plate (A).

8. The nitriding fixture for internal toothed steel sheets according to claim 7, characterized in that: The positioning mandrel (6) has axially set scale markings on its outer side wall.

9. The nitriding fixture for internal toothed steel sheets according to claim 8, characterized in that: The lower end of the positioning mandrel (6) is provided with a mounting nut (5) located on the lower side of the pressure plate (2) to fix the positioning mandrel (6).

10. A method of using the nitriding fixture for the internal toothed steel sheet as described in claim 9, characterized in that, Includes the following steps: S1: Clamping preparation: Place the lower pressure plate (2) horizontally, insert multiple rods (3) vertically into the corresponding through holes on the edge of the lower pressure plate (2), and tighten the lower locking nut (4) to fix the lower pressure plate (2) and the lower end of the rod (3); pass the positioning mandrel (6) from bottom to top through the hollow through groove (16) in the middle of the lower pressure plate (2), and tighten it to the lower side of the lower pressure plate (2) by installing nut (5); S2: Snap-fit ​​installation: Align the snap-fit ​​groove (93) of the snap-fit ​​connector (9) with the snap-fit ​​head (31) at the upper end of the rod (3), and push it in radially to complete the snap-fit, so that the snap-fit ​​connector (9) and the upper end of the rod (3) form a detachable axial connection; S3: Steel sheet stacking: Insert the inner toothed steel sheet (A) into the positioning mandrel (6) in sequence, so that the inner teeth of the inner toothed steel sheet (A) mesh with the toothed positioning groove (61) of the positioning mandrel (6), and confirm the stacking quantity through the scale on the positioning mandrel (6). S4: Pre-tightening installation: Insert the upper pressure plate (1) into the multiple connecting rods (3) so that the limiting groove (11) of the upper pressure plate (1) is aligned with the buckle connector (9); place the disc spring group (12), the inner compensation spring (15), and the outer main load spring (14) in each limiting groove (11) in sequence, and then place the shim (8); use a torque wrench to tighten the upper locking nut (7) to the rated pre-tightening force; S5: Nitriding treatment: Place the clamped fixture into the nitriding furnace, heat it to 560~580℃ and keep it at that temperature for 3~5 hours, and then introduce ammonia gas for gas nitriding treatment. S6: Disassembly and unloading: After cooling to room temperature after being taken out of the furnace, loosen the upper locking nut (7), remove the gasket (8) and the pre-tightening elastic component, and remove the upper pressure plate (1) in sequence. Take the entire stack of internal toothed steel sheets (A) out of the positioning mandrel (6) to complete the unloading.

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