CN110748524A

CN110748524A - Mechanism capable of simultaneously executing circumferential rotation and axial movement

Info

Publication number: CN110748524A
Application number: CN201911150808.7A
Authority: CN
Inventors: 郑钦元; 陈俊嘉; 陈仁贤
Original assignee: Zhejiang Chengxin Pharm & Chem Equipment Co Ltd
Current assignee: Zhejiang Chengxin Pharm & Chem Equipment Co Ltd
Priority date: 2019-11-21
Filing date: 2019-11-21
Publication date: 2020-02-04

Abstract

The invention provides a mechanism capable of simultaneously executing circumferential rotation and axial movement, and belongs to the technical field of machinery. The mechanism solves the problems that the existing mechanism capable of rotating and moving axially simultaneously is large in axial size, inconvenient to install and poor in sealing effect. This mechanism includes the outer pivot and wears to locate the downthehole adversion axle of central hole through the key cooperation, the one end of interior pivot is opened has the blind hole, sliding connection has the piston in the blind hole, the outer end of piston rod is connected with hydraulic rotary joint, hydraulic rotary joint includes outer barrel and rotates the dabber of connecting in outer barrel and linking firmly with the piston rod, the one end of dabber has the sealed dish of coaxial setting, the outer end of piston rod has the protruding edge of annular, sealed dish links firmly and seals the central hole with the terminal surface of outer pivot one end is coaxial, the protruding edge of annular sets up with sealed dish is coaxial, and the terminal surface on the protruding edge of annular is laminated mutually. The whole length of this mechanism is shorter, and installation adaptability is better, is difficult for wearing and tearing and oil leak moreover, and sealed effect is better.

Description

Mechanism capable of simultaneously executing circumferential rotation and axial movement

Technical Field

The invention belongs to the technical field of machinery, and relates to a mechanism capable of simultaneously executing circumferential rotation and axial movement.

Background

In the mechanical field, it is sometimes encountered that some mechanism is required to be able to achieve both circumferential rotation and axial movement. Because two driving sources are usually required to be simultaneously applied to the same rotating shaft in order to realize the two actions, the structure is complex, and the design difficulty is high.

The above-mentioned actions are achieved by a speed-reducing and stretching mechanism of a sizing mill with a rotary joint as disclosed in the chinese patent application (application No. 201520870169.2), which comprises a driving shaft sleeved with a transmission gear, a spline shaft extending into the driving shaft, a coupling connected to an output end of the spline shaft, and a piston rod for driving the spline shaft to stretch and stretch in the main shaft, wherein the piston rod is connected with the spline shaft through the rotary joint and the slender shaft. Therefore, the driving shaft is driven to rotate by the matching of an external power source and a transmission gear on the main shaft, the driving shaft drives the spline shaft to synchronously rotate through spline matching, and the piston rod can drive the spline shaft to move along the axial direction, so that the spline shaft can simultaneously realize circumferential rotation and axial movement. However, the piston cylinder of the structure needs to be arranged at the outer end parts of the driving shaft and the spline shaft, and the length of the piston cylinder is long, so that the sizing mill speed reduction telescopic mechanism occupies a large space, is easy to interfere in occasions with tight installation sizes, and brings great difficulty to design and installation.

The Chinese patent application (application number: 201820486320.6) discloses a rotary telescopic combined oil cylinder, which adopts a structure that a telescopic cylinder and a rotary cylinder are connected in series, a blind hole is arranged in a telescopic piston rod, the periphery of the wall of the blind hole is in transmission connection with a rotary transmission rod of the rotary cylinder through a spline, so that the rotary transmission rod can drive the telescopic piston rod to rotate, and the telescopic piston rod can move along the axial direction of the telescopic piston rod relative to the rotary transmission rod. Although this structure compares compactlyr with sizing mill speed reduction telescopic machanism, however, because the rotary cylinder can only provide limited rotary motion in rotary piston's stroke, it can't provide continuous unidirectional rotation like the motor, and application scope is less, and telescopic piston rod both will rotate relative telescopic cylinder body among this structure, and relative telescopic cylinder body is along axial displacement again, and the relative slip volume that leads to between telescopic piston rod and the telescopic cylinder body is great, and the frictional quantity between the two is great promptly, and the sealed degree of difficulty is great, the easy emergence is revealed of fluid.

Disclosure of Invention

The invention aims to solve the problems of the prior art and provides a mechanism capable of simultaneously executing circumferential rotation and axial movement, and the technical problems to be solved by the invention are as follows: how to make the mechanism that can carry out circumference rotation and axial displacement simultaneously more compact structure and sealed effect better.

The purpose of the invention can be realized by the following technical scheme: a mechanism capable of simultaneously executing circumferential rotation and axial movement comprises a rotatable outer rotating shaft with a center hole and an inner rotating shaft which is arranged in the center hole in a penetrating mode through key matching, and is characterized in that a blind hole is formed in one end of the inner rotating shaft in the axial direction, a piston which enables the blind hole to be separated into a first oil cavity and a second oil cavity is connected in the blind hole in a sliding mode in the axial direction, a piston rod is connected onto the piston, a first flow channel communicated with the first oil cavity and a second flow channel communicated with the second oil cavity are arranged on the piston rod, a hydraulic rotating joint is connected to one end, far away from the piston, of the piston rod, a third flow channel communicated with the first flow channel and a fourth flow channel communicated with the second flow channel are arranged on the hydraulic rotating joint, the hydraulic rotating joint comprises an outer cylinder body and a mandrel which is rotatably connected in the outer cylinder body and fixedly connected with the piston rod, the outer end of the piston rod is provided with an annular convex edge, the sealing disc is coaxially fixedly connected with the end face of one end of the outer rotating shaft and seals the center hole, the annular convex edge is coaxially arranged with the sealing disc, and the end face of the annular convex edge is fixedly connected with the end face of the sealing disc in a fit mode.

The outer rotating shaft of the invention can be connected with the driving piece in a transmission way to rotate, and the inner rotating shaft is connected with the outer rotating shaft in a matching way through a key, so that the inner rotating shaft can synchronously rotate along with the outer rotating shaft and simultaneously move along the axial direction relative to the outer rotating shaft. The blind hole is formed in the inner rotating shaft, the inner rotating shaft is matched with the piston and the piston rod to form a hydraulic cylinder, the piston rod is provided with a first flow channel and a second flow channel, the first flow channel and the second flow channel are used for driving the piston to move, the piston rod is connected with a hydraulic rotating joint arranged outside the outer rotating shaft, and the first flow channel and the second flow channel are communicated through the hydraulic rotating joint. Moreover, because the hydraulic cylinder structure is basically positioned in the outer rotating shaft, the axial length of the whole hydraulic cylinder structure can be designed to be shorter, and the hydraulic cylinder structure is convenient to be integrally applied to various positions with tight assembly space.

Meanwhile, the mandrel of the hydraulic rotary joint is fixedly connected with the piston rod and is fixedly connected with the end face of the outer rotating shaft at the same time, so that the mandrel, the piston rod and the outer rotating shaft form a whole, the mandrel, the piston rod and the outer rotating shaft can keep synchronous rotation, the rotation speed difference between the piston and the outer rotating shaft and the rotation speed difference between the piston and the piston rod are avoided, the friction of the piston and the piston rod caused by the rotation speed difference is avoided, the sealing effect of the hydraulic cylinder structure is better. Because the piston rod and the mandrel are fixedly connected with the sealing disc through the annular convex edge in a fit manner, the contact area between the mandrel and the piston rod is larger, the connection is more stable, the coaxiality is higher, the moving fit precision between the outer rotating shaft and the inner rotating shaft, between the piston and the inner rotating shaft and between the piston rod and the sealing cover is higher, the abrasion generated by relative sliding is less, and the sealing effect is better. In addition, the sealing disc of the mandrel seals the hydraulic cylinder structure in the central hole of the outer rotating shaft, and the hydraulic cylinder structure also plays a role in protection and dust prevention.

In the above mechanism capable of simultaneously performing circumferential rotation and axial movement, the outer cylinder is in a cylindrical shape, the inner wall of the outer cylinder is circumferentially provided with a first annular oil groove and a second annular oil groove, the first oil groove and the second oil groove are distributed along the axial direction of the outer cylinder at intervals, the outer wall of the outer cylinder is provided with a first oil hole communicated with the first oil groove and a second oil hole communicated with the second oil groove, the mandrel is provided with a first oil passage and a second oil passage, one ends of the first oil passage and the second oil passage are both located on the side wall of the mandrel and are respectively communicated with the first oil groove and the second oil groove, the other ends of the first oil passage and the second oil passage are both located on the end face of one end of the mandrel, the first oil hole, the first oil groove and the first oil passage form a third flow passage together, and the second oil hole, the second oil groove and the second oil passage form a fourth flow passage together. The outer cylinder of the hydraulic rotary joint is connected with an external oil circuit system, the outer cylinder is kept still when the outer rotating shaft rotates, the mandrel is connected with the piston rod and rotates synchronously along with the piston rod, the oil circuit between the mandrel and the outer cylinder is always communicated, and the external oil circuit realizes the control of axial expansion and contraction of the inner rotating shaft through the hydraulic rotary joint.

In foretell but simultaneous execution axial rotation and axial displacement's mechanism, the annular is protruding along laminating with sealed dish and link firmly through the bolt, it has two annular grooves that encircle first oil duct and second oil duct respectively to open on the terminal surface of sealed dish, all inlay in the annular groove and be equipped with O type circle to guarantee the sealed of oil circuit.

In foretell but simultaneous execution axial rotation and axial displacement's mechanism, be provided with three sealing washer between the inner wall of outer barrel and the outer wall of dabber, the sealing washer sets up along the length direction interval of dabber, first oil groove and second oil groove are located respectively between two adjacent sealing washers. Can guarantee the sealed effect of first oil groove and second oil groove like this, guarantee interior pivot along axial displacement's precision.

In the above mechanism capable of simultaneously performing axial rotation and axial movement, the inner wall of the central hole is fixedly provided with the guide blocks at intervals along the circumferential direction, the outer wall of the inner rotating shaft is provided with a plurality of guide grooves which correspond to the guide blocks one to one and are in sliding fit with the guide blocks, and the guide grooves extend along the axial direction of the inner rotating shaft. The guide block and the guide groove form the key fit, so that the outer rotating shaft can drive the inner rotating shaft to rotate, and meanwhile, the inner rotating shaft can move axially relative to the outer rotating shaft.

In the above mechanism capable of simultaneously performing axial rotation and axial movement, the outer rotating shaft is sleeved and fixed with a transmission member, the transmission member is a transmission gear or a belt pulley, and the guide block is located on the inner wall of the outer rotating shaft where the transmission member is located. The transmission part and the guide block are arranged on the outer rotating shaft at the same axial position basically, so that the torque of the transmission part driving the outer rotating shaft to rotate and the torque of the guide block driving the inner rotating shaft are basically the same at the axial position, the eccentric load generated between the outer rotating shaft and the inner rotating shaft is avoided, the coaxiality between the outer rotating shaft and the inner rotating shaft is higher, and the relative sliding is smoother.

In the above mechanism capable of simultaneously performing axial rotation and axial movement, the end of the inner rotating shaft, at which the blind hole is formed, is located in the central hole and has a distance from the sealing disc, the outer diameter of the sealing disc is greater than or equal to the outer diameter of the outer rotating shaft, and the outer diameter of the annular convex edge is smaller than the aperture of the central hole.

Compared with the prior art, the invention has the following advantages:

1. the structure of the invention is compact, the outer rotating shaft is connected with the inner rotating shaft through a key, a hydraulic cylinder structure is arranged between the inner rotating shaft and the outer rotating shaft and is positioned in the outer rotating shaft, so that the hydraulic cylinder structure can drive the inner rotating shaft to move along the axial direction, and simultaneously, the axial length of the structure is shortened as much as possible, and the structure has wider applicability.

2. The mandrel of the hydraulic rotary joint is provided with a sealing disc, the sealing disc is attached and fixed to the end face of the outer rotating shaft and seals the inner rotating shaft and the hydraulic cylinder structure in a center hole, and meanwhile, the piston rod is fixedly connected with the sealing disc through the annular convex edge, so that the piston rod, the piston, the inner rotating shaft, the outer rotating shaft and the mandrel can keep synchronous rotation, abrasion of all parts due to rotation speed difference is avoided, and sealing performance is guaranteed.

3. The present case structure is ingenious, sets up first runner and second runner on the piston rod to through hydraulic pressure rotary joint and outside hydraulic system intercommunication, make the piston rod can guarantee hydraulic system to the stable control of internal rotating shaft axial displacement when following outer pivot and internal rotating shaft pivoted.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic of a hydraulic cylinder configuration;

FIG. 3 is a schematic view of a hydraulic swivel;

fig. 4 is a cross-sectional view taken at a-a in fig. 1.

In the figure, 1, an outer rotating shaft; 11. a central bore; 12. a transmission member; 13. a guide block; 2. an inner rotating shaft; 21. blind holes; 21a, a first oil chamber; 21b, a second oil chamber; 22. a guide groove; 31. a piston; 32. a piston rod; 32a, a first flow passage; 32b, a second flow channel; 32c, an annular convex edge; 33. a sealing cover; 4. a hydraulic swivel joint; 41. an outer cylinder; 41a, a first oil hole; 41b, a second oil hole; 41c, a first oil groove; 41d, a second oil groove; 42. a mandrel; 42a, a first oil passage; 42b, a second oil passage; 42c, sealing disc; 5. a third flow path; 6. a fourth flow path; 7a, a sealing ring; 7b and an O-shaped ring.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.

As shown in fig. 1 and 2, a mechanism capable of simultaneously performing circumferential rotation and axial movement comprises an outer rotating shaft 1 and an inner rotating shaft 2, wherein the outer rotating shaft 1 is a cylindrical structure having a central hole 11 along an axial line, the inner rotating shaft 2 is inserted into the central hole 11 through a key, one end of the inner rotating shaft 2 is axially provided with a blind hole 21, a piston 31 and a piston rod 32 connected with the piston 31 are arranged in the blind hole 21, the piston 31 partitions the blind hole 21 into a first oil chamber 21a and a second oil chamber 21b, one end of the piston rod 32 far away from the piston 31 extends out of the inner rotating shaft 2 and is connected with a hydraulic rotary joint 4, meanwhile, a first flow passage 32a communicated with the first oil chamber 21a and a second flow passage 32b communicated with the second oil chamber 21b are arranged in the piston rod 32, the first flow passage 32a and the second flow passage 32b are respectively communicated with a third flow passage 5 and a fourth flow passage 6 on the hydraulic rotary joint 4, the third flow passage 5 and the fourth flow passage 6 of the hydraulic swivel 4 can be connected to an external hydraulic system, so that a hydraulic cylinder system is formed between the inner rotary shaft 2, the piston 31 and the piston rod 32. When the synchronous rotating device is used, the outer rotating shaft 1 can be in transmission connection with a driving source and can rotate, the hydraulic system can convey oil to the first flow passage 32a or the second flow passage 32b through the hydraulic rotating joint 4, so that the outer rotating shaft 1 can drive the inner rotating shaft 2 to synchronously rotate, and the inner rotating shaft 2 can axially move relative to the outer rotating shaft 1.

Specifically, as shown in fig. 1 to 3, a bearing and a transmission member 12 are sleeved and fixed on the outer rotating shaft 1, and the transmission member 12 is a transmission gear or a belt pulley, so that the outer rotating shaft 1 can be driven to rotate with a driving member such as a driving motor through the transmission gear or the belt pulley. The hydraulic rotary joint 4 includes an outer cylinder 41 and a mandrel 42, the outer cylinder 41 is cylindrical, the mandrel 42 is rotatably connected in the outer cylinder 41, one end of the mandrel 42 extends outward, an inner wall of the outer cylinder 41 is circumferentially provided with a first annular oil groove 41c and a second annular oil groove 41d, the first oil groove 41c and the second annular oil groove 41d are axially spaced apart from each other along the outer cylinder 41, an outer wall of the outer cylinder 41 is provided with a first oil hole 41a communicated with the first oil groove 41c and a second oil hole 41b communicated with the second oil groove 41d, the mandrel 42 is provided with a first oil passage 42a and a second oil passage 42b, one end of each of the first oil passage 42a and the second oil passage 42b is located on a side wall of the mandrel 42 and is respectively communicated with the first oil groove 41c and the second oil groove 41d, the other end of each of the first oil passage 42a and the second oil passage 42b is located on an end face of the mandrel 42 extending out of the outer cylinder 41, the first oil hole 41a, the first oil groove 41c and the first oil passage 42a together form the third flow passage 5, the second oil hole 41b, the second oil groove 41d and the second oil passage 42b together form the fourth flow passage 6, and the third flow passage 5 and the fourth flow passage 6 are ensured to be unobstructed when the spindle 42 rotates relative to the outer cylinder 41. Meanwhile, one end of the mandrel 42 extending out of the outer cylinder 41 is fixedly connected with the piston rod 32, and the first oil passage 42a is communicated with the first flow passage 32a, and the second oil passage 42b is communicated with the second flow passage 32b, so that the axial movement of the inner rotating shaft 2 is controlled.

As shown in fig. 1 to 3, a sealing cover 33 is coaxially disposed in the blind hole 21 of the inner rotating shaft 2, the sealing cover 33 is disposed at the outer end of the blind hole 21 for sealing the piston 31 in the blind hole 21, one end of the piston rod 32 passes through the sealing cover 33 and extends out of the inner rotating shaft 2, the ends of the inner rotating shaft 2, which are provided with the blind holes 21, are all disposed in the central hole 11, a certain distance is provided between the end surface of the inner rotating shaft 2, which is provided with the blind hole 21, and the end surface of the outer rotating shaft 1, which is adjacent to the end surface of the outer rotating shaft 1, of the core shaft 42, which extends out of the outer cylinder 41, is provided with a sealing disc 42c, the outer diameter of the sealing disc 42c is greater than or equal to the outer diameter of the outer rotating shaft 1, the sealing disc 42c is fixed to the end surface of the outer rotating shaft 1 by bolts, so that the sealing disc 42c seals the side opening, and the end face of the annular convex edge 32c is attached to the end face of the sealing disc 42c and fixedly connected through a bolt, so that the piston rod 32, the outer rotating shaft 1 and the mandrel 42 are fixedly connected to form a whole, the rotation synchronism of the piston rod 32, the outer rotating shaft 1, the inner rotating shaft 2 and the mandrel 42 is ensured, the circumferential friction of the piston 31 and the piston rod 32 is reduced, the abrasion is reduced, and the sealing performance is ensured. In the actual production process, because the hydraulic rotary joint 4 is usually produced by a special manufacturer, that is, the hydraulic rotary joint 4, the outer rotating shaft 1, the inner rotating shaft 2, the hydraulic cylinder structure and other components are produced by different manufacturers, the adoption of the structure is also convenient for matching and assembling the hydraulic rotary joint 4 and the components.

Furthermore, the end face of the sealing disk 42c is provided with two annular grooves surrounding the first oil passage 42a and the second oil passage 42b respectively, and the annular grooves are internally embedded with O-shaped rings 7b to avoid oil leakage.

Further, three sealing rings 7a are arranged between the inner wall of the outer cylinder 41 and the outer wall of the mandrel 42, the sealing rings 7a are arranged at intervals along the length direction of the mandrel 42, and the first oil groove 41c and the second oil groove 41d are respectively located between two adjacent sealing rings 7 a.

As shown in fig. 4, the inner wall of the central hole 11 is fixedly provided with guide blocks 13 at intervals along the circumferential direction, the outer wall of the inner rotating shaft 2 is provided with a plurality of guide grooves 22 which are in one-to-one correspondence with the guide holes and are in sliding fit with the guide holes, the guide grooves 22 extend along the axial direction of the inner rotating shaft 2, and the guide blocks 13 are positioned on the inner wall of the outer rotating shaft 1 where the transmission member 12 is arranged.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Although the terms outer shaft 1, inner shaft 2, piston 31, piston rod 32, hydraulic swivel 4, etc. are used more herein, the possibility of using other terms is not excluded. These terms are used merely to more conveniently describe and explain the nature of the present invention; they are to be construed as being without limitation to any additional limitations that may be imposed by the spirit of the present invention.

Claims

1. A mechanism capable of simultaneously executing circumferential rotation and axial movement comprises an outer rotating shaft (1) which can rotate and is provided with a center hole (11) and an inner rotating shaft (2) which is arranged in the center hole (11) in a penetrating mode in a key fit mode, and is characterized in that a blind hole (21) is formed in one end of the inner rotating shaft (2) in the axial direction, a piston (31) which enables the blind hole (21) to be separated into a first oil cavity (21a) and a second oil cavity (21b) is connected in the blind hole (21) in a sliding mode in the axial direction, a piston rod (32) is connected onto the piston (31), a first flow channel (32a) communicated with the first oil cavity (21a) and a second flow channel (32b) communicated with the second oil cavity (21b) are arranged on the piston rod (32), a hydraulic rotating joint (4) is connected to one end, far away from the piston (31), of the hydraulic rotating joint (4) is provided with a third flow channel (5) communicated with the first flow channel (32a) and a second flow 32b) The fourth runner (6) of intercommunication, hydraulic pressure rotary joint (4) include outer barrel (41) and rotate and connect in outer barrel (41) and with dabber (42) that piston rod (32) linked firmly, the one end of dabber (42) has sealed dish (42c) of coaxial setting, the outer end of piston rod (32) has annular protruding edge (32c), sealed dish (42c) link firmly and seal centre bore (11) with the coaxial laminating of the terminal surface of outward shaft (1) one end, annular protruding edge (32c) and sealed dish (42c) coaxial setting, just the terminal surface of annular protruding edge (32c) is laminated mutually with the terminal surface of sealed dish (42c) and is linked firmly.

2. The mechanism that can simultaneously perform circumferential rotation and axial movement according to claim 1, wherein the outer cylinder (41) has a cylindrical shape, the inner wall of the outer cylinder (41) is circumferentially provided with annular first and second oil grooves (41c, 41d), the first and second oil grooves (41c, 41d) are distributed at intervals in the axial direction of the outer cylinder (41), the outer wall of the outer cylinder (41) is provided with a first oil hole (41a) communicating with the first oil groove (41c) and a second oil hole (41b) communicating with the second oil groove (41d), the spindle (42) is provided with a first oil passage (42a) and a second oil passage (42b), one end of each of the first and second oil passages (42a, 42b) is located on the side wall of the spindle (42) and communicates with the first and second oil grooves (41c, 41d), respectively, the other ends of the first oil channel (42a) and the second oil channel (42b) are located on the end face of one end of the mandrel (42), the first oil hole (41a), the first oil groove (41c) and the first oil channel (42a) jointly form a third flow passage (5), and the second oil hole (41b), the second oil groove (41d) and the second oil channel (42b) jointly form a fourth flow passage (6).

3. The mechanism capable of simultaneously performing circumferential rotation and axial movement according to claim 2, wherein the annular flange (32c) is attached to the sealing disk (42c) and fixedly connected by a bolt, two annular grooves surrounding the first oil passage (42a) and the second oil passage (42b) are formed in the end surface of the sealing disk (42c), and the O-rings (7b) are embedded in the annular grooves.

4. The mechanism capable of simultaneously performing circumferential rotation and axial movement according to claim 3, wherein three sealing rings (7a) are arranged between the inner wall of the outer cylinder (41) and the outer wall of the mandrel (42), the sealing rings (7a) are arranged at intervals along the length direction of the mandrel (42), and the first oil groove (41c) and the second oil groove (41d) are respectively located between two adjacent sealing rings (7 a).

5. The mechanism capable of simultaneously performing circumferential rotation and axial movement according to claim 1 or 2, wherein the inner wall of the central hole (11) is fixedly provided with guide blocks (13) at intervals along the circumferential direction, the outer wall of the inner rotating shaft (2) is provided with a plurality of guide grooves (22) which correspond to the guide blocks (13) in a one-to-one and are in sliding fit, and the guide grooves (22) extend along the axial direction of the inner rotating shaft (2).

6. Mechanism capable of performing circumferential rotation and axial movement simultaneously as claimed in claim 5, characterized in that a transmission member (12) is sleeved and fixed on the outer rotating shaft (1), the transmission member (12) is a transmission gear or a belt pulley, and the guide block (13) is located on the inner wall of the outer rotating shaft (1) where the transmission member (12) is located.

7. Mechanism capable of performing both circumferential rotation and axial movement according to claim 2 or 3, characterized in that the end of the inner rotating shaft (2) provided with the blind hole (21) is located in the central hole (11) and spaced from the sealing disc (42c), the outer diameter of the sealing disc (42c) is larger than or equal to the outer diameter of the outer rotating shaft (1), and the outer diameter of the annular convex edge (32c) is smaller than the diameter of the central hole (11).