Hollow fiber rod rotary joint with closed loop fluid circulation

Abstract

The application discloses a hollow wire screw rotary joint with closed loop fluid circulation and belongs to the technical field of machine tool parts. The rotary joint comprises a shell fixing assembly, a rotating shaft assembly, a mechanical seal assembly, a fluid passage assembly and a sealing anti-seepage assembly. A quick plug connector is integrated in the base and communicates with the flow guide pipe to form a same-side closed loop fluid circulation flow channel. A first O-shaped ring is arranged in the three-joint gap formed by the fixing ring, the base and the bearing outer ring, and the elastic expansion force generated by bidirectional compression is used for circumferentially fixing and sealing the bearing outer ring. A Y-shaped sealing ring is arranged between the static ring seat and the base, the lip of the Y-shaped sealing ring faces the backflow cavity side and forms surface contact with the matching surface to block the medium capillary climbing. The application solves the problems of bearing outer ring follow-up, medium seepage corrosion bearing and low integration degree of the flow channel in the prior art and is suitable for various hollow wire screw working conditions requiring cooling or lubrication.

Description

Technical Field

[0001] This invention relates to a rotary joint, and more particularly to a rotary joint applied to a hollow lead screw that enables closed-loop circulation conveying of cooling or lubricating media entering and exiting from the same side, belonging to the technical field of machine tool components. Background Technology

[0002] In precision CNC machine tools, industrial robots, and other automated equipment, hollow lead screws are the core components for achieving high-precision linear transmission. To control the temperature rise of the lead screw during high-speed operation and ensure the lubrication of the internal transmission pairs, a rotary joint is typically used to deliver cooling or lubricating media into the inner hole of the hollow lead screw.

[0003] Chinese patent CN208729285U discloses a rotary joint for center cooling of a ball screw. This design enables fluid to enter and exit on the same side, but some shortcomings have been found during use. Its structure still has the following areas for optimization: 1. Regarding the fixing of bearings; In this design, the bearing outer ring is fixed solely by an interference fit. Under vibration conditions, this hard-contact fixing method tends to generate microscopic gaps and cause the outer ring to rotate. To prevent the bearing outer ring from rotating under high-frequency vibration, the industry's long-standing design approach has focused on improving the reliability of hard contacts, commonly employing methods such as pin locking, outer ring locking grooves, or increased interference fit. While these methods offer some anti-rotation effects, they introduce problems such as high machining precision requirements, assembly difficulties, and increased costs. Against this industry backdrop, a prevailing perception has emerged that rubber elastomers, such as O-rings, lack sufficient stiffness to provide adequate circumferential locking force and can only serve as auxiliary seals or vibration dampers, not as the primary means of preventing bearing outer ring rotation. Consequently, there have been few attempts in the field to use elastomers as the main anti-rotation method for bearing outer rings.

[0004] 2. Regarding the setting of static seal; In this design, only one O-ring is used for sealing between the stationary ring seat and the housing. The resulting near-line contact is insufficient to effectively prevent the slow creep of fluid caused by capillary action within the tiny fit gap. It should be noted that in the field of rotary joints, the failure of static seals has long been habitually attributed to the wear or aging of the O-ring. However, capillary creep of the medium along the tiny fit gap, as an independent and persistent failure mode, has not been fully recognized or specifically addressed, thus masking the root cause of the failure for a long time. Existing designs do not include specific blocking structures for this phenomenon.

[0005] 3. Regarding the layout of the fluid interface; This solution uses external adapter fittings to connect the pipeline, which increases the potential external leakage points and is also bulky.

[0006] Therefore, it is necessary to improve the existing rotary joints to break free from the constraints of the aforementioned design inertia and fundamentally solve these long-neglected problems. Summary of the Invention

[0007] This invention aims to provide a hollow screw rotary joint with closed-loop fluid circulation, which solves the problem of bearing outer ring rotation under vibration conditions caused by simply relying on interference fit to fix the bearing outer ring. It effectively blocks the capillary climb of the medium along the static mating surface, thus solving the problem of bearing being easily corroded by the medium. By reducing external leakage points and reducing product volume, the integration of the flow channel is improved.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a hollow screw rotary joint with closed-loop fluid circulation, comprising a housing fixing assembly, a rotating shaft assembly, a mechanical seal assembly, a fluid passage assembly, and a sealing and seepage prevention assembly; The housing fixing assembly includes a base and a top cover. The base and the top cover are fixedly connected and enclose an installation cavity. The side wall of the base has a fluid inlet and a fluid outlet. The interior of the base has an internal flow channel that connects the fluid inlet to the installation position of the built-in quick connector. The rotating shaft assembly includes a hollow rotating shaft, which is rotatably mounted in the mounting cavity via at least one set of bearings. The upper end of the rotating shaft extends out of the upper cover for external connection to a hollow lead screw. The mechanical seal assembly includes a rotating ring and a stationary ring that fit together. The rotating ring is fixedly installed on the lower part of the rotating shaft and rotates synchronously with the rotating shaft. The stationary ring is fixedly disposed in the inner cavity of the base and remains stationary. Both the rotating ring and the stationary ring have a flow hole at their center, and the inner hole of the rotating shaft is coaxially connected with the flow hole. The fluid passage assembly includes a built-in quick-connect connector and a flow guide tube. The built-in quick-connect connector is fixedly installed inside the base and is connected to the fluid inlet through the internal flow channel. One end of the flow guide tube is connected to the built-in quick-connect connector, and the other end is coaxially inserted into the inner hole of the rotating shaft and extends into the hollow screw, for directional delivery of fluid to the far end of the hollow screw cavity. A sealing ring is provided between the flow guide tube and the built-in quick-connect connector. The sealing and seepage-proof assembly includes a second O-ring, a third O-ring, and a dustproof seal disposed between the upper cover and the rotating shaft; the second O-ring is fitted onto the threaded part of the upper part of the rotating shaft for static sealing at the connection position between the rotating shaft and the hollow screw; the third O-ring is disposed between the mating end faces of the base and the upper cover for static sealing and dustproofing of the shell mating surface. The lower end of the flow passage of the stationary ring is connected to the return cavity inside the base, and the return cavity is connected to the fluid outlet; During operation, the fluid enters the internal flow channel of the base through the fluid inlet, and is transported to the hollow screw through the built-in quick-connect connector and guide tube. Then, it flows back from the internal cavity of the hollow screw through the inner hole of the rotating shaft, and flows into the return cavity through the central flow holes of the moving ring and stationary ring in sequence, and finally flows out from the fluid outlet, forming a closed-loop circulation channel in which the fluid enters and exits on the same side of the screw.

[0009] The housing fixing assembly also includes a fixing ring, which is a part independent of the upper cover and the base. The fixing ring is located on the lower end side of the bearing and supports the lower end face of the outer ring of the bearing. The outer periphery of the fixing ring is radially engaged with the inner wall of the upper cover. The lower end face of the outer ring of the bearing, the upper outer edge stepped surface of the fixing ring, and the inner wall of the upper cover form an L-shaped annular fitting gap that is axially and radially connected. A first O-ring is provided in the gap. The first O-ring simultaneously bears axial compression from the fixing ring and radial compression from the outer ring of the bearing and the fixing ring. It circumferentially fixes and seals the outer ring of the bearing through bidirectional elastic tension force to prevent its rotation.

[0010] The mechanical seal assembly also includes a stationary ring seat, wherein the stationary ring is fixedly embedded in the inner hole of the stationary ring seat; the stationary ring seat is installed in the inner cavity of the base, and a Y-shaped sealing ring is provided between the outer wall of the stationary ring seat and the inner wall of the base; the lip of the Y-shaped sealing ring faces the reflux cavity side, and the lip of the Y-shaped sealing ring is in surface contact with the mating surface, which is used to prevent the fluid in the reflux cavity from capillarily climbing upward along the mating gap of the outer wall of the stationary ring seat.

[0011] The base has a threaded mounting hole inside, and the built-in quick connector is fixed in the threaded mounting hole by tightening the thread. The threaded mounting hole is connected to the internal flow channel.

[0012] Furthermore, an elastic element and a circumferential positioning element are provided between the base and the stationary ring seat; the elastic element is installed in the mounting hole of the base and is used to push the stationary ring seat upward so that the sealing end faces of the rotating ring and the stationary ring always remain in tight contact and to compensate for the wear of the end faces; the circumferential positioning element is inserted into the positioning hole of the base and the stationary ring seat and is used to restrict the circumferential rotation of the stationary ring seat.

[0013] Furthermore, the bearings are provided in two sets, arranged vertically along the axis of the shaft and fitted onto the outer circumference of the shaft; the outer wall of the shaft is provided with an annular groove, and a retaining ring is installed in the groove to axially limit the inner ring of the bearing.

[0014] Furthermore, the circumferential positioning component is a cylindrical pin, the surface of which is coated with adhesive and has an interference fit with the positioning hole.

[0015] Furthermore, the elastic element is a cylindrical helical spring, and at least three sets are provided, which are evenly distributed circumferentially in the mounting holes of the base.

[0016] Furthermore, the lip of the Y-shaped sealing ring faces the reflux cavity side, achieving self-tightening sealing using the medium pressure.

[0017] Furthermore, the end of the guide tube is provided with a limiting structure, and the length extending into the hollow screw is not less than twice the diameter of the screw's inner hole.

[0018] Furthermore, the reflux cavity is formed by stepping up the inner diameter of the upper mounting cavity in the inner cavity of the base, which is used to buffer and reduce the flow rate of the reflux fluid.

[0019] Furthermore, the moving ring is fixedly installed on the lower part of the rotating shaft via a moving ring seat, the moving ring and the moving ring seat are interference-fitted, and the moving ring seat and the rotating shaft are coaxially and fixedly connected.

[0020] Furthermore, the outer wall of the guide tube and the inner wall of the rotating shaft are in clearance fit, with a clearance of 0.2-0.5 mm on one side.

[0021] Furthermore, the base and the top cover are both made of aluminum alloy; the rotating shaft, the moving ring seat, and the stationary ring seat are all made of stainless steel.

[0022] Furthermore, the retaining ring is made of aluminum alloy.

[0023] Furthermore, the guide tube is a pressure-resistant fluid tube made of PA11 material.

[0024] Furthermore, the first O-ring is used simultaneously to circumferentially fix the outer ring of the bearing and to seal the mating clearance at that location.

[0025] Furthermore, the assembly compression rate of the first O-ring is 15%-25%.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves fluid entry and exit and closed-loop circulation on the same side of the lead screw by opening a fluid inlet and outlet on the side wall of the base, combined with internal flow channels, built-in quick-connect couplings, and guide pipes. This design eliminates the need for piping layout at both ends of the lead screw, saving installation space, and the medium can be recycled and reused in a closed loop, reducing operating costs.

[0027] 2. This invention uses a retaining ring independent of the top cover and base, and a first O-ring subjected to bidirectional compression within the three-way gap. The circumferential friction generated by the O-ring's elastic expansion force secures the outer ring of the bearing. Under vibration test conditions of 50Hz frequency and 2g acceleration, the outer ring of the bearing of this invention did not rotate, while existing interference fit designs exhibited observable circumferential displacement under the same conditions. Furthermore, the first O-ring serves both locking and sealing functions, achieving a dual purpose with a single ring and simplifying the structure.

[0028] 3. This invention addresses the long-neglected independent failure mode of capillary creep along the static mating surface. By placing a Y-shaped sealing ring with its lip facing the return cavity between the outer wall of the stationary ring seat and the inner wall of the base, its surface contact characteristics effectively cut off the capillary creep channel in the minute mating clearance. After 1000 hours of continuous operation, disassembly and inspection revealed that the bearing cavity of this invention remained dry, and the grease showed no emulsification or deterioration. In contrast, existing single O-ring solutions showed significant media penetration and corrosion under the same conditions, proving that this solution effectively blocks capillary creep and protects the bearing from corrosion.

[0029] 4. This invention eliminates the need for external adapters by directly fixing the quick-connect connector inside the base with threads, reducing leakage points and making the structure more compact.

[0030] 5. In this invention, the bidirectional locking and sealing of the first O-ring reduces the anti-creep pressure on the Y-type sealing ring; the Y-type sealing ring blocks the main creep path, protecting the elasticity of the bearing and the first O-ring; the built-in quick-connect fitting reduces the intrusion of external contaminants and reduces the wear of impurities on the various seals. These three elements mutually protect each other, forming a virtuous cycle, which increases the mean time between failures (MTBF) of the entire machine to 2.2 times that of the prior art. Attached Figure Description

[0031] Figure 1 This is a schematic cross-sectional view of the overall structure of Embodiment 1 of the present invention.

[0032] Figure 2 This is a schematic diagram of the overall exploded structure of Embodiment 1 of the present invention.

[0033] Figure 3 This is a schematic diagram of the fluid closed-loop circulation direction in Embodiment 1 of the present invention.

[0034] In the diagram: 1 is the rotating shaft, 2 is the stationary ring, 3 is the guide tube, 4 is the second O-ring, 5 is the top cover, 6 is the retaining ring, 7 is the bearing, 8 is the fixed ring, 9 is the moving ring seat, 10 is the cylindrical pin, 11 is the stationary ring seat, 12 is the spring, 13 is the base, 14 is the built-in quick-connect coupling, 15 is the Y-type sealing ring, 16 is the third O-ring, 17 is the first O-ring, 18 is the moving ring, 19 is the sealing ring, and 20 is the dustproof oil seal. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example

[0036] like Figures 1 to 3As shown, this embodiment provides a standard double-bearing hollow screw rotary joint, which has an overall axisymmetric rotary structure and mainly consists of a housing fixing assembly, a rotating shaft assembly, a mechanical seal assembly, a fluid passage assembly, and a sealing and leak-proof assembly. The rated applicable speed is ≤3000rpm, the working pressure range is 0.1-1.0MPa, and the applicable medium temperature is 5-80℃. It can be adapted to various fluid media such as cooling water, emulsions, and lubricating oil.

[0037] The housing fixing assembly includes a base 13, a top cover 5, and a fixing ring 8. The base 13 is a stepped cylindrical shape made of 6061-T6 aluminum alloy, with a PT1 / 4 internally threaded hole on each of its left and right side walls, serving as the fluid inlet and outlet, respectively. The base 13 has a multi-level stepped internal cavity, from top to bottom: a bearing mounting position, a stationary ring seat mounting position, and a return flow cavity. A connecting oblique hole serves as an internal flow channel between the fluid inlet on the side wall and the internal quick-connect fitting mounting position; the wall thickness in this area is locally thickened to ensure the flow channel wall thickness meets pressure resistance requirements. The return flow cavity is formed by a stepped expansion of the inner diameter of the upper stationary ring seat mounting cavity, with a significantly larger lateral cross-sectional area than the upper mounting cavity. The return flow cavity has a diameter of 45mm, while the upper mounting cavity has a diameter of 32mm, resulting in an expansion ratio of approximately 1.4. This reduces the fluid velocity from approximately 2.5m / s to 0.8m / s, acting as a buffer to decrease the velocity of the returning fluid. The upper surface of the base 13 has six small holes evenly distributed circumferentially for installing the spring 12 and the cylindrical pin 10, respectively. The upper surface of the base 13 also has an annular groove for placing the third O-ring 16. The upper cover 5 is also made of 6061-T6 aluminum alloy and is locked to the upper surface of the base 13 by four sets of internal hexagonal screws, forming a closed mounting cavity. The center of the upper cover 5 has a stepped through hole for the rotating shaft 1 to pass through, and the stepped surface can axially limit the upper end of the outer ring of the upper bearing 7. The retaining ring 8 is a 6061-T6 aluminum alloy annular component independent of the upper cover 5 and the base 13, and is clamped and fixed between the upper cover 5 and the base 13. When the upper cover 5 is locked, the retaining ring 8 axially presses the outer ring of the bearing 7, while simultaneously constraining the radial position of the bearing 7. The sidewall of the retaining ring 8, the supporting end face of the base 13, and the outer wall of the bearing 7's outer ring together form an annular fitting gap with space in both the axial and radial directions. A first O-ring 17, made of fluororubber with a wire diameter of 1.8 mm and an outer diameter of 35 mm, is installed within this gap. When the upper cover 5 presses against the retaining ring 8, the first O-ring 17 is simultaneously subjected to axial compression from the retaining ring 8 and radial compression from the bearing's outer ring and the inner wall of the retaining ring, generating a bidirectional elastic tightening force. This achieves circumferential fixation and sealing of the bearing's outer ring, preventing it from rotating. The O-ring's assembly compression rate is controlled between 15% and 25%. After being compressed bidirectionally in the axial and radial directions, it generates an elastic tightening force, filling the assembly play between the three components, ensuring a gapless fit between the bearing's outer ring, the retaining ring, and the base, completely locking the bearing's outer ring. Simultaneously, the O-ring also serves as an auxiliary static seal, preventing the medium below from seeping upwards along the assembly gap.

[0038] The rotating shaft assembly includes a hollow rotating shaft 1, two sets of bearings 7, and a retaining ring 6. The rotating shaft 1 is made of 304 stainless steel, with a hollow through-hole structure, smooth inner wall, and an inner diameter of 8mm. The upper end of the rotating shaft 1 has an M16×1.5 external thread for threaded connection to an external hollow lead screw, with an effective thread length of not less than 12mm. An annular sealing groove is provided at the root of the thread for installing a second O-ring 4. The lower end of the rotating shaft 1 has a stepped shaft for installing a moving ring seat 9. The lower end face is axially positioned and fitted with the moving ring seat 9 to ensure coaxiality. The two sets of bearings 7 are 6003ZZ double-sided dustproof deep groove ball bearings, arranged vertically around the outer circumference of the rotating shaft 1. The inner and outer rings respectively mate with the rotating shaft 1 and the retaining ring 8, forming a double-support rotational support to jointly bear the radial load, ensuring smooth rotation and coaxiality of the shaft, reducing radial runout, and improving the contact accuracy of the sealing end faces. The retaining ring 6 is a 17mm shaft elastic retaining ring, which is installed in the annular groove on the outer wall of the rotating shaft 1. This groove is opened between the mounting positions of the two sets of bearings to axially limit the inner ring of the bearing, prevent the bearing and the rotating shaft from moving up and down, and ensure the axial position accuracy of the internal components.

[0039] The mechanical seal assembly is used to achieve dynamic sealing of the rotating end face and forms a central return channel. It includes a rotating ring seat 9, a rotating ring 18, a stationary ring seat 11, and a stationary ring 2. The rotating ring seat 9 is a cylindrical part made of 304 stainless steel, fixedly fitted on the lower step of the rotating shaft 1, and rotates synchronously with the shaft 1. The rotating ring 18 is made of high-purity graphite, with excellent self-lubricating properties and a low coefficient of friction. It is fixedly embedded in the inner hole of the rotating ring seat 9 through an interference fit, and has a flow hole with a diameter of 8mm in its center. The lower end face of the rotating ring 18 is a precision-polished sealing end face with a flatness ≤0.9μm and a roughness Ra≤0.2μm, meeting the first-class precision standard for mechanical seals. It fits tightly with the upper end face of the stationary ring 2 to form a sealing pair. The stationary ring seat 11 is a stepped cylindrical part made of 304 stainless steel, installed in the inner cavity of the base 13. The upper outer circle of the ring 11 has a clearance of H7 / g6 (maximum clearance 0.041mm) between it and the inner cavity of the base 13, ensuring that the compression of the Y-ring lip is 0.3-0.5mm. A blind hole for accommodating the spring 12 is provided circumferentially on the lower end face. The stationary ring 2 is made of reaction-sintered silicon carbide, which has high hardness and excellent wear resistance. It is fixedly embedded in the inner hole of the stationary ring seat 11 by an interference fit, remaining stationary. The center of the stationary ring 2 also has an 8mm diameter flow hole. Its upper end face is a precision-polished sealing end face, which fits tightly with the lower end face of the rotating ring 18 to form a rotary sealing pair. This sealing pair allows fluid to pass through the central hole while preventing fluid leakage from the gap in the rotary end face. A Y-shaped sealing ring 15, made of fluororubber with a hardness of HS75, is provided between the outer wall of the stationary ring seat 11 and the inner wall of the base 13. The lip of the Y-shaped sealing ring 15 faces the lower return cavity, and its lip has a certain width, forming a surface contact with the mating surface. When the medium in the reflux chamber attempts to leak upwards through the tiny gap between the stationary ring seat 11 and the base 13, the lip of the Y-shaped sealing ring 15 physically interrupts the continuity of the capillary channel. Simultaneously, the medium pressure acts on the inner side of the lip, forcing it to open more tightly and adhere to the inner wall of the base, creating a self-tightening effect. After 1000 hours of static aging test at 80°C, its permanent deformation rate of the lip height is only 8%, still maintaining the elasticity required for effective sealing. Four sets of springs 12 and circumferential positioning pins are also provided between the base 13 and the stationary ring seat 11. Spring 12 is a stainless steel cylindrical helical spring with a wire diameter of 0.4mm × outer diameter of 3mm × free length of 10mm. Four sets of springs are evenly installed in the mounting holes on the upper end face of the base 13 along the circumference. At the working height, it provides a total thrust of about 18N, keeping the specific pressure of the dynamic and static ring end faces within the range of 0.2-0.4MPa, ensuring a tight seal, and automatically compensating for the wear of the end faces to ensure long-term sealing performance.The circumferential positioning component is a cylindrical pin 10 with a specification of M3×10. Two sets are set in total and are symmetrically installed in the positioning holes of the base 13 and the stationary ring seat 11. The surface of the cylindrical pin is coated with Loctite 243 glue and is interference-fitted with the positioning hole to achieve circumferential anti-rotation positioning of the stationary ring seat, prevent the stationary ring from rotating synchronously with the moving ring, and prevent loosening under strong vibration conditions.

[0040] The fluid flow assembly includes a built-in quick-connect fitting 14 and a flow guide tube 3. The built-in quick-connect fitting 14 is a commercially available standard part, model QSM-1 / 8-6-I, indicating that its interface thread is 1 / 8 inch and it is suitable for hoses with an outer diameter of 6mm. The base 13 has a specially machined threaded mounting hole to match this fitting. The built-in quick-connect fitting 14 is tightened into this mounting hole via its external thread. Loctite 243 adhesive is applied to the thread to prevent loosening. The installation torque is 8-10 N·m. The bottom of this threaded mounting hole is connected to the internal flow channel of the base 13. The flow guide tube 3 is a pressure-resistant fluid tube made of PA11 material, with an outer diameter of 6mm and an inner diameter of 4mm. It features temperature resistance, pressure resistance, and aging resistance. One end of the tube is inserted and fixed to the built-in quick-connect fitting 14, with an insertion depth of not less than 8mm. A sealing ring 19 is provided between the guide tube 3 and the built-in quick-connect fitting 14. This sealing ring 19 is an O-ring located in the inner hole of the quick-connect fitting, forming a radial static seal on the outer wall of the guide tube 3 to prevent fluid leakage from the root. The other end of the guide tube 3 extends upward, passing sequentially through the central flow hole of the stationary ring 2, the moving ring 18, and the inner hole of the rotating shaft 1, finally extending into the far end of the internal cavity of the externally connected hollow lead screw. Its length extending into the lead screw is not less than twice the diameter of the lead screw's inner hole, directing the inlet fluid to the far end of the lead screw cavity, ensuring that the fluid can fill the entire inner cavity of the lead screw before flowing back, maximizing heat exchange and lubrication effects. The outer wall of the guide tube 3 and the inner wall of the rotating shaft 1 are clearance-fitted, with a single-sided clearance of 0.2-0.5 mm, ensuring no friction occurs while providing sufficient annular flow area for the returning fluid. The impact force of low-speed fluid on the lip of the Y-type sealing ring 15 is significantly reduced. Under the same working conditions, the lip wear of the Y-type ring is 0.03 mm after 2000 hours of operation when there is a return cavity, and 0.07 mm when there is no return cavity (straight-through structure), extending the service life by 57%.

[0041] The sealing and leak-proof assembly includes a second O-ring 4, a third O-ring 16, a first O-ring 17, a Y-type sealing ring 15, a sealing ring 19, and a dustproof oil seal 20. The second O-ring 4 is a fluororubber O-ring with an outer diameter of 18mm, fitted into the sealing groove at the root of the thread on the upper end of the shaft 1. It provides a static seal at the connection between the shaft and the hollow screw, preventing media leakage from the threaded gap and blocking external dust and impurities from entering the connection area. The third O-ring 16 is a fluororubber O-ring with an outer diameter of 36mm, installed in the annular groove on the upper surface of the base 13. It provides a planar static seal and dustproof seal at the mating surface between the base and the top cover, protecting internal components from external environmental corrosion. The dustproof oil seal 20 is installed between the central stepped hole of the top cover 5 and the shaft 1, preventing external dust, cutting fluid, and other impurities from entering the bearing cavity and extending bearing life. In addition, threadlocker is applied to all threaded connections to prevent loosening and provide auxiliary sealing; the spare threaded holes on the base and top cover can be sealed with hexagonal plugs to prevent dust and impurities from entering the flow channel.

[0042] The key process parameters involved in this embodiment are as follows: The fit clearance between the inner cavity of the base and the outer circle of the stationary ring seat is H7 / g6 (maximum clearance 0.041mm), ensuring that the compression of the Y-ring lip is 0.3-0.5mm.

[0043] Fit between the shaft and the inner ring of the bearing: j6, ensuring no loosening after heat fitting.

[0044] Flatness of the sealing end face of the dynamic and static rings: ≤0.9μm, roughness Ra≤0.05μm (ultra-precision machining).

[0045] The roughness of the inner wall of the retaining ring should be Ra≤1.6μm to avoid scratching the O-ring.

[0046] All aluminum alloy parts (base, top cover, retaining ring) undergo T6 heat treatment, with a hardness ≥95HBW.

[0047] The coaxiality of the mating surface between the outer circle of the shaft and the inner ring of the bearing is ≤0.005mm; the coaxiality between the inner hole of the shaft and the outer circle is ≤0.01mm; after assembly, the radial runout measured at the end of the shaft (10mm from the end face) is ≤0.03mm.

[0048] The assembly process in this embodiment is as follows: Screw the built-in quick-connect connector 14 into the threaded mounting hole inside the base 13, pre-apply glue to the threads, and tighten with a torque of 8-10 N·m; install the spring 12 and the cylindrical pin 10 into the corresponding holes on the upper surface of the base 13, and apply glue to the cylindrical pin for fixation.

[0049] Insert the Y-shaped sealing ring 15 into the outer circular groove of the stationary ring seat 11, and then press the stationary ring 2 into the inner hole of the stationary ring seat 11 to form the stationary ring seat assembly. Install the entire assembly into the inner cavity of the base 13, ensuring that the positioning pin is aligned and the spring is in place.

[0050] The lower bearing 7 is press-fitted into the lower bearing mounting position of the rotating shaft 1, and the retaining ring 6 is installed for axial positioning; then the upper bearing 7 is press-fitted into the upper mounting position of the rotating shaft 1. The moving ring 18 is pressed into the moving ring seat 9, and then the moving ring seat 9 is fitted onto the lower end of the rotating shaft 1 to form the rotor assembly.

[0051] Place the first O-ring 17 into the triple gap between the bearing support end face of the base 13 and the fixed ring 8; install the fixed ring 8; install the rotor assembly into the inner cavity of the base, so that the outer ring of the bearing falls into the inner wall of the fixed ring 8.

[0052] Place the third O-ring 16 into the annular groove on the upper surface of the base 13, fasten the top cover 5, and tighten the four sets of fixing screws evenly.

[0053] Insert the second O-ring 4 into the sealing groove at the root of the thread at the upper end of the shaft 1; install the dustproof oil seal 20 between the center hole of the upper cover 5 and the shaft 1.

[0054] Insert the guide tube 3 downward from the upper port of the rotating shaft 1, through each center hole, until its tail end contacts the end face of the built-in quick connector 14, and stop after confirming that it is inserted in place.

[0055] The working principle of this embodiment is as follows: During operation, the cooling or lubricating medium enters through the fluid inlet on the side wall of the base 13, flows through the internal flow channel of the base 13 into the built-in quick-connect connector 14, and is then directionally transported to the far end of the internal cavity of the hollow screw via the guide pipe 3. After the medium fills the inner cavity of the screw, it flows back along the annular space between the inner wall of the screw and the guide pipe 3, and flows downward through the inner hole of the rotating shaft 1. Subsequently, the medium flows through the central flow holes of the moving ring 18 and the stationary ring 2 in sequence into the return cavity below the base 13. Due to the increased cross-sectional area of ​​the return cavity, the fluid velocity decreases, and the impact force on the Y-type sealing ring 15 is significantly reduced. Finally, the medium flows out smoothly from the fluid outlet on the side wall of the base 13 and connects to the external circulation system, completing the closed-loop circulation on the same side. During the entire rotation operation, the rotating shaft 1, the moving ring seat 9, and the moving ring 18 rotate synchronously with the hollow screw, while the stationary ring seat 11, the stationary ring 2, and the base 13 remain stationary. The sealing end faces of the rotating ring 18 and the stationary ring 2 are always tightly fitted under the preload of the spring 12, achieving a reliable seal on the rotating end face. The Y-type sealing ring 15 blocks the path of the medium to seep upward into the bearing cavity, and the first O-ring 17 locks the outer ring of the bearing to prevent it from rotating and assists in sealing. The multiple structures work together to ensure the long-term stable operation of the rotary joint. Example

[0056] This embodiment provides a single-bearing, light-load hollow lead screw rotary joint, suitable for light-load small lead screws with diameters of 12-16mm, rated applicable speed ≤2000rpm, and working pressure range of 0.1-0.6MPa. It is suitable for light-load working conditions with limited space, such as small automated equipment and miniature precision machine tools. The main difference from Embodiment 1 is: Only one set of bearings 7 is provided, using a 6003ZZ deep groove ball bearing, installed at the upper part of the rotating shaft 1 to bear the radial load. The lower part of the rotating shaft 1 achieves auxiliary radial positioning through the cooperation of the moving ring seat 9 and the stationary ring 2 to ensure rotational coaxiality.

[0057] The retaining ring 6 is removed, and the axial positioning of the bearing inner ring is achieved bidirectionally through the shoulder on the rotating shaft 1 and the upper end face of the moving ring seat 9.

[0058] The inner hole height of the retaining ring 8 is shortened accordingly, and it only mates with the outer ring of a single bearing; the specifications of the first O-ring 17 and the size of the triple clearance are adjusted accordingly, and the bidirectional compression locking structure is still adopted to ensure that the outer ring does not rotate under single bearing conditions.

[0059] Spring 12 is configured in three groups, evenly distributed along the circumference, to provide a stable end face thrust.

[0060] The overall axial dimension of the base 13 and the top cover 5 is reduced by about 25% compared with that of Embodiment 1, making it suitable for light-load conditions with limited axial installation space.

[0061] The remaining structures, assembly relationships, and working principles of this embodiment are basically the same as those of Embodiment 1, and will not be repeated here. Example

[0062] This embodiment is a large-size, heavy-duty hollow screw rotary joint, suitable for high-load hollow screws with diameters of 32-50mm, rated applicable speed ≤1500rpm, and working pressure range 0.2-1.5MPa. It is suitable for heavy-duty working conditions such as heavy-duty CNC machine tools and large gantry machining centers. The main difference from Embodiment 1 is: The overall dimensions of the base 13, top cover 5, and retaining ring 8 are enlarged proportionally. The bearing 7 adopts a deep groove ball bearing of model 6007ZZ, which increases the load-bearing capacity by 2.5 times and still adopts a double-row structure. The corresponding first O-ring 17 is adjusted to an outer diameter of 62mm and a wire diameter of 2.0mm to provide stronger radial tension force and ensure that the outer ring of the bearing does not rotate under heavy load conditions.

[0063] The springs 12 are set in six groups, evenly distributed along the circumference, to provide greater axial thrust, adapt to higher working pressure, and ensure stable specific pressure of the end face seal under high pressure.

[0064] The stationary ring 2 is made of silicon carbide sintered under normal pressure, while the moving ring 18 is made of antimony-impregnated graphite, which has stronger wear resistance and impact resistance, making it suitable for heavy-duty impact conditions.

[0065] The specifications of the guide tube 3 have been adjusted to an outer diameter of 8mm and an inner diameter of 6mm, increasing the fluid flow rate by 70% to meet the high-flow cooling and lubrication requirements of large-diameter lead screws; the built-in quick-connect connector 14 has been adjusted to be compatible with the 8mm pipe diameter.

[0066] The volume of the reflux chamber is increased accordingly to reduce fluid turbulence under high flow rates and ensure the stability of the sealing end face.

[0067] The remaining structures, assembly relationships, and working principles of this embodiment are basically the same as those of Embodiment 1, and will not be repeated here. Example

[0068] This embodiment is a high-speed, light-load hollow lead screw rotary joint, suitable for high-speed precision lead screws with diameters of 12-20mm, rated applicable speed ≤8000rpm, and working pressure range of 0.1-0.8MPa. It is suitable for high-speed drilling and tapping centers, precision electronic processing equipment, and other high-speed operating scenarios. The main difference from Embodiment 1 is: Bearing 7 uses two sets of ceramic ball deep groove ball bearings, which have low centrifugal force, low temperature rise, and stronger stability at high speeds; the bearing adopts a pre-tightening installation method to eliminate internal clearance and reduce vibration and noise at high speeds.

[0069] Both the rotating ring 18 and the stationary ring 2 are made of silicon carbide, resulting in a lower coefficient of friction, less frictional temperature rise at high speeds, and a longer service life. The sealing end face is ultra-precision polished, resulting in higher flatness and stable fit under high-speed rotation.

[0070] The rotating shaft 1 adopts a hollow and lightweight design to reduce rotational inertia and improve high-speed response; the outer cylindrical surface of the rotating shaft is ground with high precision, and the coaxiality error is controlled within 2μm to ensure the runout accuracy of high-speed rotation.

[0071] An auxiliary O-ring is added to the upper part of the stationary ring seat to form a three-stage sealing system of double Y-rings and O-rings, which enhances the sealing reliability under high-speed conditions and prevents high-speed airflow from carrying the medium into the bearing cavity.

[0072] The guide tube 3 is made of lighter PFA material with a smoother inner wall and less fluid resistance, making it suitable for the rapid circulation requirements of high-speed equipment.

[0073] The remaining structures, assembly relationships, and working principles of this embodiment are basically the same as those of Embodiment 1, and will not be repeated here. Example

[0074] This embodiment is suitable for extreme operating conditions with pressure ≤2.5MPa and speed ≤10000rpm, such as ultra-high-speed machining centers and turbine test benches. It further enhances upon embodiment 4: Both the dynamic and static rings are made of pressureless sintered silicon carbide with a hardness of ≥2500HV and wear resistance that is 5 times higher than that of graphite.

[0075] A second Y-shaped sealing ring is added and installed back-to-back to form a double self-tightening seal, increasing the pressure resistance to 3.0MPa.

[0076] The bearing uses a hybrid ceramic ball (Si3N4) and low-temperature bearing grease, which reduces the temperature rise by 30%.

[0077] The guide tube is made of stainless steel corrugated pipe, which can adapt to high and low temperature alternation (-40℃~150℃).

[0078] An elastic pad is added between the fixing ring and the base to absorb high-frequency vibration.

[0079] Tests showed that this embodiment operated continuously for 500 hours under 2.5MPa / 10000rpm conditions with a leakage rate of <0.5mL / h, a bearing temperature rise of ≤35℃, and a rotational speed of 0, meeting the requirements of extreme operating conditions.

[0080] To verify the technical effects of the present invention, the prototype manufactured based on Example 1 (the present invention) and the comparative prototype manufactured entirely according to patent CN208729285U (the comparative example) were tested under the same conditions. The test conditions were: rotation speed 3000 rpm, medium pressure 0.6 MPa, water medium, and vibration at a frequency of 50 Hz and an acceleration of 2g applied on an electric vibration table.

[0081] Long-term sealing performance test: Continuous operation for 3000 hours, with leakage and bearing cavity humidity recorded every 500 hours (monitored using a humidity sensor). Results are as follows:

[0082] After 3000 hours, disassembly and inspection revealed that the bearing grease showed no emulsification or corrosion, and the wear on the sealing end face was only 0.015 mm. This proves that the graded sealing system of this invention can effectively prevent media creep for a long period of time.

[0083] Bearing anti-rotation comparison test: After running for 100 hours under the above vibration conditions, the outer ring of the comparative bearing showed observable circumferential displacement, while the outer ring of the bearing of the present invention did not rotate. Furthermore, to verify the irreplaceable nature of bidirectional compression, an O-ring comparison structure subjected only to radial compression (eliminating the axial clamping effect of the retaining ring) was prepared. Under the same conditions, its circumferential friction force was approximately 40% of that of the bidirectional compression structure, posing a risk of rotation. A sweep frequency vibration test (10-200Hz, acceleration 2g) was conducted on an electric vibration table, and the angular displacement of the bearing outer ring relative to the retaining ring was observed. Simultaneously, compared with the comparative structure (interference fit), the rotation angle of the present invention was 0° across the entire frequency range.

[0084] Cooling efficiency test: A rotary joint was installed on a hollow lead screw (25mm in diameter, 800mm in length), and 20℃ cooling water was introduced at a flow rate of 2L / min. The steady-state temperature rise of the lead screw and nut assembly at 1000rpm was measured. Comparison scheme: no cooling, comparative rotary joint.

[0085]

[0086] The present invention improves the cooling efficiency by 37% compared to the comparative example (the temperature rise is reduced from 18.2℃ to 11.5℃), and by 70% compared to no cooling. It also reduces thermal elongation by 69%, significantly improving positioning accuracy.

[0087] Operating noise comparison: The A-weighted sound pressure level of the rotary joint was measured in a semi-anechoic chamber at 3000 rpm and 0.6 MPa. The comparative noise was 58 dB, with a peak near 500 Hz in the spectrum (abnormal noise from bearing rotation); the noise of this invention was 51 dB, with a smooth and wide spectrum, no abnormal noise, and a noise reduction of 7 dB.

[0088] Sealing adaptability to different media: Four media were tested: clean water, emulsion (5%), No. 32 hydraulic oil and cutting oil. The leakage was recorded after 500 hours of operation at 0.6MPa / 3000rpm.

[0089] Y-type sealing rings are well-suited to various media, and exhibit less leakage in oily media.

[0090] Ease of maintenance verification: Five technicians performed simulated maintenance (replacing internal seals) on the comparative example and the present invention respectively, and recorded the time from disassembly to reassembly.

[0091] This invention reduces maintenance time by 57% and requires no special tools, significantly reducing operation and maintenance costs.

[0092] High and low temperature cycling test: The rotary joint was placed in a temperature chamber and cycled between -20℃ and 80℃ (one cycle every 24 hours, with high and low temperatures maintained for 6 hours each, and a temperature rise / fall rate of 2℃ / min). The sealing performance was tested after 10 consecutive cycles. Results: All prototypes were tested immediately after cycling at 0.6MPa pressure, with a leakage rate ≤0.1mL / min and no performance degradation. This demonstrates that the O-rings and Y-rings maintain good elasticity over a wide temperature range.

[0093] Pressure shock test: A pulse pressure of 0→1.2MPa was applied to the rotary joint (rise time 0.1s, holding pressure for 2s, release), and the seals were inspected after 100,000 cycles. Results: No tearing of the Y-ring lip, no extrusion of the O-ring, and wear of the end face sealing pair ≤0.005mm. This demonstrates that the graded sealing system has excellent resistance to pressure shock.

[0094] Overall lifespan testing: Based on failure data from 10 prototypes operating continuously for 3000 hours (0 failures), the lower limit of MTBF was estimated using the Weibull distribution (90% confidence level): MTBF ≥ 6200 hours. The historical MTBF of the comparative structure under the same operating conditions was 2800 hours (based on field data from 20 units). The MTBF of this invention is 2.2 times that of the comparative example, indicating that the combined application of multiple improvements significantly enhances product reliability.

[0095] The first O-ring compression ratio gradient test showed that at a compression ratio of 10%, the rotation rate was 12%, indicating average sealing performance; at 15%-25%, the rotation rate was 0%, indicating reliable sealing; and at 30%, the assembly resistance was too high, and the O-ring was easily sheared and damaged. Therefore, the optimal compression ratio range is 15%-25%, which balances locking effect, sealing performance, and assemblability.

[0096] Y-ring lip interference limits: When the interference is <0.2mm, the seal is insufficient under low pressure; when it is >0.7mm, assembly is difficult and frictional resistance is high. 0.3-0.5mm is preferred.

[0097] Limits for single-sided clearance of the guide tube: <0.15mm, friction may occur under shaft runout; >0.6mm, the reduced return cross-sectional area leads to increased pressure loss and decreased cooling efficiency. 0.2-0.5mm is preferred.

[0098] Spring pressure limit: When the end face pressure is <0.15MPa, the sealing pair may separate under low pressure; when it is >0.5MPa, the frictional power consumption is large and the temperature rises. 0.2-0.4MPa is preferred.

[0099] Radial runout control of the shaft and anti-friction design of the guide tube: To ensure that no friction occurs between the guide tube and the inner wall of the shaft during long-term operation, the following requirements are set for the machining and assembly of the shaft: the coaxiality of the mating surface between the outer circle of the shaft and the inner ring of the bearing is ≤0.005mm; the coaxiality between the inner hole of the shaft and the outer circle is ≤0.01mm; after assembly, the radial runout measured at the end of the shaft (10mm from the end face) is ≤0.03mm. Actual measurements show that under the above control conditions, the minimum clearance between the guide tube and the inner wall of the shaft is still ≥0.15mm (initial clearance 0.2mm minus maximum runout 0.03mm minus thermal expansion 0.02mm), providing sufficient safety margin. After 1000 hours of continuous operation, disassembly and inspection revealed no friction marks on the outer wall of the guide tube.

[0100] Y-ring permanent deformation test: A Y-ring (fluororubber, hardness HS75) was installed in the fit gap between the stationary ring seat and the base, with a compression rate of 15%. After standing at 80℃ for 1000 hours, it was removed and the change in cross-sectional dimensions was measured. Results: The permanent deformation rate of the lip height was 8%, still maintaining the elasticity required for effective sealing (industry standard requirement ≤15%). Under a water pressure of 1.0MPa, the leakage was still ≤0.3mL / h. This proves that the Y-ring can maintain its sealing performance under long-term static compression.

[0101] The design formula for the bidirectional compression of the first O-ring: The first O-ring (wire diameter d) is assembled in the triple gap, and the axial compression is... = (Axial displacement after the retaining ring is tightened) - (Gap height), Radial compression amount = (Inner diameter of the retaining ring - Outer diameter of the bearing outer ring) - d. Axial compression ratio = Radial compressibility = Total compressive energy = axial compressive energy + radial compressive energy > twice the unidirectional compressive energy. According to this formula, for an O-ring with d = 1.8 mm, ≈0.18mm, The diameter is approximately 0.22 mm, and the total compression rate is approximately 22%, which falls within the preferred range.

[0102] All of the above-mentioned fixing methods are conventional technologies in this field, and those skilled in the art can choose according to specific working conditions, all of which fall within the protection scope of this invention.

Claims

1. A hollow-fiber rotary joint with closed-loop fluid circulation, characterized in that, It includes a housing fixing assembly, a rotating shaft assembly, a mechanical seal assembly, a fluid passage assembly, and a sealing and leak-proof assembly; The housing fixing assembly includes a base (13) and a top cover (5). The base (13) and the top cover (5) are fixedly connected and enclose to form an installation cavity. The side wall of the base (13) is provided with a fluid inlet and a fluid outlet. The interior of the base (13) is provided with an internal flow channel that connects the fluid inlet to the installation position of the built-in quick connector (14). The rotating shaft assembly includes a hollow rotating shaft (1), which is rotatably mounted in the mounting cavity via at least one set of bearings (7). The upper end of the rotating shaft (1) extends out of the upper cover (5) for external connection of a hollow lead screw. The mechanical seal assembly includes a rotating ring (18) and a stationary ring (2) that fit together. The rotating ring (18) is fixedly installed on the lower part of the rotating shaft (1) and rotates synchronously with the rotating shaft (1). The stationary ring (2) is fixedly installed in the inner cavity of the base (13) and remains stationary. Both the rotating ring (18) and the stationary ring (2) have flow holes in their centers. The inner hole of the rotating shaft (1) is coaxially connected with the flow holes. The fluid passage assembly includes a built-in quick-connect connector (14) and a guide tube (3). The built-in quick-connect connector (14) is fixedly installed inside the base (13) and is connected to the fluid inlet through the internal flow channel. One end of the guide tube (3) is connected to the built-in quick-connect connector (14), and the other end is coaxially inserted into the inner hole of the rotating shaft (1) and extends into the hollow screw, for directional delivery of fluid to the far end of the hollow screw cavity. A sealing ring (19) is provided between the guide tube (3) and the built-in quick-connect connector (14). The sealing and seepage prevention assembly includes a second O-ring (4), a third O-ring (16), and a dustproof seal (20) disposed between the upper cover (5) and the rotating shaft (1); the second O-ring (4) is fitted onto the threaded part on the upper part of the rotating shaft (1) for static sealing at the connection position between the rotating shaft (1) and the hollow screw; the third O-ring (16) is disposed between the mating end face of the base (13) and the upper cover (5) for static sealing and dust prevention at the shell mating surface; The lower end of the flow hole of the stationary ring (2) is connected to the return cavity inside the base (13), and the return cavity is connected to the fluid outlet; During operation, the fluid enters the internal flow channel of the base (13) from the fluid inlet, and is transported to the hollow screw through the built-in quick connector (14) and guide tube (3); then flows back from the internal cavity of the hollow screw through the inner hole of the rotating shaft (1), and flows into the return cavity through the central flow hole of the moving ring (18) and stationary ring (2) in sequence, and finally flows out from the fluid outlet, forming a closed-loop circulation channel in which the fluid enters and exits on the same side of the screw.

2. The hollow-fiber rotary joint with closed-loop fluid circulation according to claim 1, characterized in that, The housing fixing assembly also includes a fixing ring (8), which is a part independent of the upper cover (5) and the base (13). The fixing ring (8) is located on the lower end side of the bearing (7) and supports the lower end face of the outer ring of the bearing (7). The outer periphery of the fixing ring (8) is radially engaged with the inner wall of the upper cover (5). The lower end face of the outer ring of the bearing (7), the upper outer edge step surface of the fixing ring (8), and the inner wall of the upper cover (5) form an L-shaped annular fitting gap that is axially and radially connected. A first O-ring (17) is provided in the gap. The first O-ring (17) simultaneously bears the axial compression from the fixing ring (8) and the radial compression from the outer ring of the bearing and the fixing ring (8). It circumferentially fixes and seals the outer ring of the bearing (7) through bidirectional elastic tension force to prevent it from rotating.

3. The hollow screw rotary joint with closed-loop fluid circulation according to claim 1, characterized in that, The mechanical seal assembly also includes a stationary ring seat (11), wherein the stationary ring (2) is fixedly embedded in the inner hole of the stationary ring seat (11); the stationary ring seat (11) is installed in the inner cavity of the base (13), and a Y-shaped sealing ring (15) is provided between the outer wall of the stationary ring seat (11) and the inner wall of the base (13); the lip of the Y-shaped sealing ring (15) faces the reflux cavity side, and the lip of the Y-shaped sealing ring (15) is in surface contact with the mating surface, which is used to prevent the fluid in the reflux cavity from capillarily climbing upward along the mating gap of the outer wall of the stationary ring seat (11).

4. The hollow screw rotary joint with closed-loop fluid circulation according to claim 3, characterized in that, An elastic element and a circumferential positioning element are provided between the base (13) and the stationary ring seat (11); The elastic element is installed in the mounting hole of the base (13) to push the stationary ring seat (11) upward so that the sealing end face of the moving ring (18) and the stationary ring (2) always keeps in close contact and compensates for the wear of the end face. The circumferential positioning element is inserted into the positioning holes of the base (13) and the stationary ring seat (11) to restrict the circumferential rotation of the stationary ring seat (11).

5. The hollow screw rotary joint with closed-loop fluid circulation according to claim 1, characterized in that, The base (13) has a threaded mounting hole inside, and the built-in quick connector (14) is fixed in the threaded mounting hole by screwing in the thread. The threaded mounting hole is connected to the internal flow channel.

6. The hollow screw rotary joint with closed-loop fluid circulation according to claim 2, characterized in that, The bearing (7) is provided in two sets, arranged vertically along the axis of the rotating shaft (1) and fitted on the outer circumference of the rotating shaft (1); the outer wall of the rotating shaft (1) is provided with an annular groove, and a retaining ring (6) is installed in the groove. The retaining ring (6) is used to axially limit the inner ring of the bearing (7).

7. The hollow screw rotary joint with closed-loop fluid circulation according to claim 4, characterized in that, The circumferential positioning component is a cylindrical pin (10), the surface of which is coated with adhesive and has an interference fit with the positioning hole.

8. The hollow screw rotary joint with closed-loop fluid circulation according to claim 4, characterized in that, The elastic element is a cylindrical helical spring (12), and at least three sets are provided, which are evenly distributed in the mounting holes of the base (13) along the circumference.

9. The hollow screw rotary joint with closed-loop fluid circulation according to claim 1, characterized in that, The outer wall of the guide tube (3) and the inner wall of the rotating shaft (1) are in clearance fit, with a single-sided clearance of 0.2-0.5 mm.

10. The hollow screw rotary joint with closed-loop fluid circulation according to claim 2, characterized in that, The assembly compression rate of the first O-ring (17) is 15%-25%.

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