CN117515165A - Multistage combined rotary shaft sealing device capable of self-adaptively centering - Google Patents

Abstract

A multi-stage combined rotary shaft sealing device capable of self-adaptively centering relates to the technical field of rotary shaft sealing, and comprises a fixed end and a sliding end which are connected with two ends of a rotary shaft, wherein the fixed end and the sliding end are both connected with a device shell and the rotary shaft; the sliding end comprises a pre-sealing structure, an expansion joint, a multi-stage combined sealing structure and a self-supporting bearing assembly which are sequentially connected along the axis of the rotary shaft, wherein the pre-sealing structure, the expansion joint, the multi-stage combined sealing structure and the self-supporting bearing assembly are all sleeved outside the rotary shaft, a shaft sleeve is fixed outside the rotary shaft, the self-supporting bearing assembly comprises a self-aligning roller bearing and a positioning shell, an inner ring of the self-aligning roller bearing is connected with the shaft sleeve, an outer ring of the self-aligning roller bearing is connected with the positioning shell, the positioning shell is connected with the multi-stage combined sealing structure, and the expansion joint is of a flexible structure. The use requirement of the shaft seal of the long-span rotary shaft under severe working conditions is met.

Description

Multistage combined rotary shaft sealing device capable of self-adaptively centering

Technical Field

The invention belongs to the technical field of rotating shaft sealing, and particularly relates to a multistage combined rotating shaft sealing device capable of self-adaptively centering.

Background

The mechanical seal means a device for preventing fluid leakage, which is formed by at least one pair of end surfaces perpendicular to the rotation axis and keeping fit and sliding relatively under the action of the fluid pressure and the elasticity or magnetic force of the compensation mechanism and the cooperation of the auxiliary seal. The main structure of the device comprises a stationary ring, a movable ring, a gland, a push ring, a spring, a positioning ring, a shaft sleeve, a movable ring sealing ring and a stationary ring sealing ring. According to different standards, the two-way valve can be divided into balanced type and unbalanced type, built-in type and built-out type, single end face and double end face, inward flow and outward flow and other different types.

Mechanical seals are often used as seals for industrial equipment, where the reliability requirements for the seals are higher for equipment with a rotating shaft structure. The single sealing method has limitation in use, so the mechanical seal adopted by the rotary shaft is generally of a multi-stage sealing structure so as to ensure the stability and reliability of the shaft seal.

In addition, because the working condition of the equipment using the rotary shaft seal is sometimes worse, under the conditions of long span and large load of the rotary shaft of the equipment, the stability of the sealing device in centering is higher, and the existing shaft seal structure faces the problem of sealing failure caused by axial movement and radial runout.

The multistage mechanical seal structure for the pump disclosed in the authority number CN217874172U adopts a multistage mechanical seal structure, and the positioning mode is to match and position by utilizing the annular positioning groove on the surface of the movable ring and the positioning rod on the fixed ring, and the positioning mode can be subjected to radial force when the shaft is displaced, so that the sealing failure and the damage of the sealing structure are caused.

The existing shaft seal structure has poor self-adaptability to deformation of equipment, and the consistency of the sealing effect cannot be ensured. The existing shaft seal structure integrating multiple sealing modes has stricter requirements on precision, so that the optimal sealing effect is expected to be realized, and the shaft seal structure is difficult to use under severe working conditions and on a long-span shaft.

Disclosure of Invention

The technical problem that this application solved is: the utility model provides a but overcoming the not enough of prior art, provides a multistage combination swivel shaft sealing device of self-adaptation centering, satisfies the operation requirement of the bearing seal of long-span swivel shaft under abominable operating mode.

The technical scheme provided by the application is as follows:

the multistage combined rotary shaft sealing device capable of self-adaptive centering comprises a fixed end and a sliding end which are connected with two ends of a rotary shaft, wherein the fixed end and the sliding end are both connected between an equipment shell and the rotary shaft; the sliding end comprises a pre-sealing structure, an expansion joint, a multi-stage combined sealing structure and a self-supporting bearing assembly which are sequentially connected along the axis of the rotary shaft, wherein the pre-sealing structure, the expansion joint, the multi-stage combined sealing structure and the self-supporting bearing assembly are all sleeved outside the rotary shaft, a shaft sleeve is fixed outside the rotary shaft, the self-supporting bearing assembly comprises a self-aligning roller bearing and a positioning shell, an inner ring of the self-aligning roller bearing is connected with the shaft sleeve, an outer ring of the self-aligning roller bearing is connected with the positioning shell, the positioning shell is connected with the multi-stage combined sealing structure, and the expansion joint is of a flexible structure.

In one implementation of the sealing device, the sliding end further comprises a positioning chuck structure connected between the device housing and the pre-sealing structure, the positioning chuck structure being coaxial with the swivel shaft when tightened.

In one implementation of the sealing device, the pre-sealing structure comprises a pre-sealing ring and a multi-stage static sealing structure connected to the inner side of the pre-sealing ring, the multi-stage static sealing structure is in contact with the outer wall of the rotating shaft, and the pre-sealing ring is fixedly connected with the positioning chuck structure.

In one implementation of the sealing device, the expansion joint includes a bellows, and an inner end flange and an outer end flange connected to two ends of the bellows, the inner end flange is fixedly connected to the pre-sealing structure, and the outer end flange is fixedly connected to the multi-stage combined sealing structure.

In one implementation of the sealing device, the multi-stage combined sealing structure comprises a fixed sleeve and a dynamic sealing structure connected between the fixed sleeve and the shaft sleeve, wherein the fixed sleeve is fixedly connected with the expansion joint and the positioning shell.

In one implementation of the sealing device, the positioning housing comprises a bearing cover and a bearing seat cover which are fixedly connected, the bearing cover is fixedly connected with the expansion joint and the fixed sleeve, the bearing cover and the bearing seat cover are sleeved on the outer side of the bearing, and a gap is reserved between one end of the inner side of the bearing cover and the end face of the outer ring of the bearing for sliding positioning of the bearing.

In one implementation of the sealing device, a cavity is formed between the two end surfaces of the bearing and the positioning shell, and a sealing structure is arranged between the shaft sleeve and the positioning shell so as to isolate the inner cavity of the positioning shell from the outside.

In one implementation of the sealing device, the sealing structure includes two bearing part sealing rings, one bearing part sealing ring is used for sealing and fixing a gap between the sleeve and the shaft sleeve, and the other bearing part sealing ring is used for sealing a gap between the shaft sleeve and the bearing seat cover, so that cavities at two ends of the bearing are isolated from the outside.

In one implementation of the sealing device, the bearing housing is provided with an isolation gas inlet, one end of the isolation gas inlet is communicated with the cavities at two ends of the bearing, and the other end of the isolation gas inlet is communicated with the outer wall of the bearing housing and is connected with an isolation gas source.

In one implementation of the sealing device, the fixed end comprises a positioning chuck structure, a pre-sealing structure, a multi-stage combined sealing structure and a self-supporting bearing assembly which are sequentially and fixedly connected along the axis of the rotating shaft, the positioning chuck structure, the pre-sealing structure, the multi-stage combined sealing structure and the self-supporting bearing assembly are all sleeved outside the rotating shaft, a shaft sleeve is fixed outside the rotating shaft, the self-supporting bearing assembly comprises a aligning roller bearing and a positioning shell, an inner ring of the aligning roller bearing is connected with the shaft sleeve, an outer ring of the aligning roller bearing is connected with the positioning shell, and the positioning shell is connected with the multi-stage combined sealing structure.

In summary, the present application at least includes the following beneficial technical effects:

(1) The dynamic seal and the static seal are combined, so that the sealing reliability is ensured to the greatest extent, and meanwhile, the sealing forms of the multi-stage sealing structures can be combined and matched according to working conditions, so that the sealing structure has excellent adaptability;

(2) The shell of the sealing device can absorb the expansion amount and the jumping amount of the rotating shaft of the equipment under various working conditions through the deformation of the expansion joint part, so that the integral matching precision of the sealing device is always stable within a design range, the self-adaptive centering can be realized when the equipment operates, and the reliability and the service life of the sealing device are ensured;

(3) The second seal, namely the dynamic seal mechanism is arranged in the gap between the expansion joint and the rotary shaft, so that the working environment requirement of the dynamic seal mechanism can be met, the reliability of the dynamic seal mechanism is ensured, the whole length of the seal device can be reduced to the greatest extent, and the integrity and the working stability of the seal device are enhanced; (the structure is described in detail in the schemes or embodiments)

(4) The bearing can be adjusted according to the actual working condition and used as an auxiliary bearing of the rotating shaft, so that the sealing device can be supported, the outer ring is connected with the sealing device shell to play an auxiliary supporting role on the rotating shaft, the running stability of equipment is further enhanced, the stability of the sealing device is enhanced, the bearing can also be used as a main bearing of the rotating shaft, and the bearing can be adjusted and selected according to specific load;

(5) A certain gap is reserved between the proximal end of the bearing and the device shell, and the self-adaptive sliding adjustment can be performed according to the deformation adjustment of the expansion joint during working, so that the self-adaptive centering function of the device can be achieved, and the overall reliability of the sealing device is ensured;

(6) A space is reserved between the end face of the bearing and the device shell, and a sealing structure is arranged at the bottom of the space, so that annular sealing spaces are respectively formed at the two ends of the bearing, the stability of the working environment of the bearing can be ensured, the stable operation of the sealing device is ensured, and sealing gas can be introduced into the space as required to strengthen the sealing effect of the device.

Drawings

FIG. 1 is a schematic view of a sliding end seal arrangement;

FIG. 2 is a schematic view of a fixed end seal.

Reference numerals illustrate: 1. the positioning chuck structure, 2, the pre-sealing structure, 3, the expansion joint, 3-1 and the inner end flange; 3-2, an outer end flange; 3-3, corrugated pipe; 4. the multi-stage combined sealing structure comprises a multi-stage combined sealing structure, 5, a self-supporting bearing assembly, 5-1, a bearing housing, 5-2, a shaft sleeve, 5-3, a bearing, 5-4, a sealing ring at the bearing, 5-5, a bearing seat cover, 5-6, an isolation gas inlet, 6, an equipment shell, 7 and a rotary shaft.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are illustrated in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

The embodiment of the application discloses multistage combination rotary shaft sealing device capable of self-adaptive centering, which is respectively installed at the joint of an equipment shell 6 needing sealing and a rotary shaft 7 as shown in fig. 1 and 2, and is generally installed at two ends of the rotary shaft, and comprises a sliding end and a fixed end. Wherein the sliding end seal only has more expansion joints 3 than the fixed end seal.

As shown in fig. 1, the sliding end comprises a positioning chuck structure 1, a pre-sealing structure 2, an expansion joint 3, a multi-stage combined sealing structure 4 and a self-supporting bearing assembly 5 which are sequentially connected and sleeved outside a rotating shaft 7. The positioning chuck structure 1, the pre-sealing structure 2, the expansion joint 3, the multi-stage combined sealing structure 4 and the self-supporting bearing assembly 5 are connected through bolts to form a stable structure, so that the integrity and the stability of the sealing device are ensured, the sequential loading and unloading of the multi-stage device can be realized, and the efficiency and the economical efficiency of the maintenance and the replacement of a vulnerable part can be greatly improved. As shown in FIG. 2, the fixed end sequentially comprises a positioning chuck structure, a pre-sealing structure, a multi-stage combined sealing structure and a self-supporting bearing structure, and all the components are connected by bolts, so that the sealing device can continuously and stably realize the sealing function of the rotary shaft equipment.

The positioning chuck structure 1 comprises a chuck shell and a chuck mechanism connected to the chuck shell, the chuck mechanism is a three-jaw chuck or a four-jaw chuck, the chuck shell of the positioning chuck structure 1 is connected with the side wall 6 of the equipment shell through bolts, the positioning chuck structure is fixedly connected with the equipment shell 6, the chuck mechanism can be synchronously adjusted through screw threads, and therefore the radial positions of the positioning sealing device and the rotating shaft 7 can assist the centering and fixing of the sealing device. When the sealing device is assembled and disassembled, the chuck mechanism clamps the rotary shaft 7, so that synchronous radial adjustment of positioning can be realized, and when the sealing device is assembled and disassembled, the shell of the sealing device can be accurately positioned in the centering way with the rotary shaft 7 through the adjustment of the position of the sealing device, and further, the functions of auxiliary positioning and auxiliary supporting are realized.

As shown in fig. 1, the pre-sealing structure 2 is connected with the positioning chuck structure 1 through bolts, and the structure can adopt a combination seal of a plurality of modes such as labyrinth seal, brush seal, isolation air seal and the like to form preliminary limitation on fluid escaping from the interior of the equipment, and form preliminary seal when the rotating shaft 7 works. In this embodiment, the pre-sealing structure 2 is a brush seal, and specifically includes a pre-sealing ring and bristles connected to an inner ring of the pre-sealing ring, where the bristles contact with an outer wall of the rotating shaft 7, and the pre-sealing ring is connected to the positioning chuck structure 1 through a bolt.

As shown in fig. 1, the expansion joint 3 comprises a bellows 3-3, and an inner end flange 3-1 and an outer end flange 3-2 which are connected to two ends of the bellows 3-3, wherein the inner end flange 3-1 and the pre-sealing structure 2 can be connected through bolts, and the outer end flange 3-2 is connected with the multi-stage combined sealing structure 4 and the self-supporting bearing assembly 5 through bolts.

The self-supporting bearing assembly 5 comprises a bearing housing 5-1, a bearing 5-3 and a bearing seat cover 5-5, wherein a shaft sleeve 5-2 is sleeved on the outer side of the rotary shaft 7, the shaft sleeve 5-2 is fixedly connected with the rotary shaft 7, an inner ring of the bearing 5-3 is connected with the shaft sleeve 5-2, the bearing housing 5-1 is sleeved on the outer side of an outer ring of the bearing 5-3, the inner diameter of the end, close to the multistage combined sealing structure 4, of the bearing housing 5-1 is smaller than the diameter of the outer ring of the bearing 5-3, the bearing seat cover 5-5 is located at one end, deviating from the multistage combined sealing structure 4, of the bearing housing 5-1, and the bearing seat cover 5-5 is connected with the bearing housing 5-1 through bolts. The bearing 5-3 arranged on the shaft sleeve 5-2 on the rotary shaft 7 can be used as a supporting structure of the sealing device, a bearing cover structure is arranged outside the bearing 5-3, the inner ring of the bearing 5-3 is matched with the bearing cover 5-1 in a positioning way through the shaft sleeve 5-2 and rotates along with the rotary shaft 7, the outer ring of the bearing 5-3 is matched with the bearing cover 5-1 in a positioning way, and the bearing cover 5-1, the bearing cover 5-2 and the bearing cover 5-5 form a bearing seat structure together. The sleeve 5-2 simultaneously serves to protect the rotary shaft 7. The self-aligning roller bearing 5-3 is used as a supporting structure of the sealing device, an inner ring of the self-aligning roller bearing is tightly matched with the shaft sleeve 5-2 and rotates along with the rotary shaft, and an outer ring of the self-aligning roller bearing is contacted with a static ring (the bearing housing 5-1, the bearing housing cover 5-5, the expansion joint 3, the pre-sealing structure 2 and the positioning chuck structure 1) to bear the static ring during operation.

As shown in fig. 1, the multi-stage combined sealing structure 4 includes a fixed sleeve and a dynamic sealing structure connected between the fixed sleeve and the shaft sleeve 5-2. The fixing sleeve comprises a sleeve and a connecting flange integrally connected to the end of the sleeve, and bolts penetrate through the outer end flange 3-2 and the fixing sleeve and are connected to the bearing housing 5-1 in a threaded manner, so that the outer end flange 3-2, the fixing sleeve and the bearing housing 5-1 are connected together. The dynamic seal is located in the gap between the expansion joint 3 and the rotary shaft 7, which arrangement minimizes the axial dimension of the seal, so that the rotary shaft does not have to add more length to the installation seal, enhancing its operational stability by reducing its span. The multi-stage combined sealing structure 4 can adopt various sealing structures such as labyrinth sealing, brush sealing, isolation gas sealing and the like, and can also continuously input sealing gas or sealing liquid, and structures such as an isolation gas inlet are added.

In this embodiment, the dynamic seal structure includes two VD sealing rings that are dorsad, and two VD sealing rings are located between fixed sleeve and axle sleeve 5-2, and the centre of two VD sealing rings is provided with the spring, and the outside of two VD sealing rings sets up static annular seal, annular seal and fixed sleeve fixed connection. The space formed between the two VD sealing rings can be filled with isolation gas.

As shown in FIG. 1, the bearing 5-3 is positioned with the bearing housing 5-1 through the shaft sleeve 5-2, the inner ring of the bearing 5-3 is positioned radially through the positioning fit of the shaft sleeve 5-2, the inner ring of the bearing 5-3 rotates along with the rotary shaft 7, the end face of the inner ring of the bearing 5-3 is limited in the axial direction through the shaft sleeve 5-2, the outer ring of the bearing 5-3 is positioned with the bearing housing 5-1, and the end face of the outer ring of the bearing 5-3 is positioned axially through the bearing cap 5-5. One end of the bearing housing is contacted with the outer ring of the outer end face of the bearing and positioned, and a gap is reserved between the other end of the bearing housing and the inner end face of the bearing, so that the bearing can be slidably positioned. When the rotary shaft 7 expands, the shaft sleeve 5-2 and the bearing 5-3 move axially along with the rotary shaft 7, and when the bearing seat cover 5-5 and the bearing cover 5-1 cannot move completely synchronously with the bearing 5-3, the arrangement of the clearance ensures that the bearing seat cover 5-5 and the bearing cover 5-1 cannot directly extrude with the end face of the outer ring of the bearing 5-3 to cause structural damage, so that the axial position adjustment can be carried out when the rotary shaft 7 expands, the stability of the structure is ensured not to be influenced by the deformation of the rotary shaft 7, and the sealing effect of the sealing device is ensured to be stable.

Because the bearing 5-3 has the aligning effect, the influence caused by the expansion and the jumping of the rotating shaft can be counteracted during the working, the bearing 5-3 adopts an aligning roller bearing, a certain adjusting effect can be realized, and the expansion joint 3 can be matched to absorb a part of jumping deformation quantity, so that the self-supporting bearing assembly 5 is ensured to be always stable in the whole and matched with the rotating shaft 7, and the multistage combined sealing structure 4 also realizes the self-adaptive centering function of the rotating shaft 7 through the connection of the bearing housing 5-1.

As shown in fig. 1, the bearing housing 5-1 is connected with the outer end flange 3-2 of the expansion joint 3 through bolts, the end flange is always kept in a self-adaptive centering state with the rotary shaft 7, the inner end flange 3-1, the pre-sealing structure 2, the positioning chuck structure 1 and the equipment shell side wall 6 are sequentially fixed through bolts, the inner end flange 3-1 is always kept in stable fit with the equipment shell side wall 6, the bellows 3-3 structure of the expansion joint 3 plays a role in adjusting, so that when expansion and runout generated by the equipment shell side wall 6 and the rotary shaft 7 are asynchronous, the multi-stage combined sealing structure 4 still realizes self-adaptive centering positioning, and the sealing device always keeps running stability and is not easy to damage.

Cavities are respectively formed between the two end surfaces of the bearing 5-3 and the bearing seat structure, and sealing structures are arranged at the combined parts of the cavities and the outside, so that the inner cavity of the bearing seat is isolated from the outside, the functions of dust prevention and corrosion prevention are achieved, and the internal bearing is protected. The sealing structure is two bearing part sealing rings 5-4, one bearing part sealing ring 5-4 is used for sealing and fixing a gap between the sleeve and the shaft sleeve 5-2, and the other bearing part sealing ring 5-4 is used for sealing a gap between the shaft sleeve 5-2 and the bearing seat cover 5-5, so that cavities at two ends of the bearing 5-3 are isolated from the outside, the bearing is in an environment-stable sealing space, the dustproof and anti-corrosion effects are achieved, the internal bearing is protected, an isolation gas inlet 5-6 is formed in the bearing cover 5-1, one end of the isolation gas inlet 5-6 is communicated with the cavities at two ends of the bearing 5-3, the other end of the isolation gas inlet is communicated with the outer wall of the bearing cover 5-1, isolation gas can be introduced into the space through the isolation gas inlet 5-6, and the working stability of the device is further improved.

As shown in fig. 2, compared with the movable end, the fixed end is not provided with the expansion joint 3, the fixed sleeve of the multistage combined sealing structure is directly connected with the sealing structure through a bolt, and other structures are the same as the movable end.

In the structure of the fixed end, the bearing has a supporting function on the whole sealing device and can also support the rotating shaft, and optionally, according to working conditions, the bearing can be used as a secondary bearing of the rotating shaft to play a role of auxiliary support and also can be used as a main supporting bearing of the rotating shaft, and different choices can be made according to different functions and the form of the bearing required by the working conditions.

The implementation principle of the application is as follows:

one end of the rotary shaft 7 is fixed with the side wall 6 of the equipment shell through a fixed end, the other end is fixed with the side wall 6 of the equipment shell through a movable end, the fixed end enables the rotary shaft 7 to be in positioning connection with the side wall 6 of the shell to form firm fit, the rotary shaft 7 is stably supported through the bearing 5-3, and when the rotary shaft 7 is subjected to expansion deformation, the end does not displace along with the expansion deformation, so that the sealed operation of the end is ensured to be stable; the movable end can be adaptively adjusted along with the deformation of the rotary shaft 7 through the expansion joint 3 structure, so that the sealing part is not influenced, and the stable operation of the whole sealing structure is realized.

When the shaft is heated to expand axially or radial jumping quantity is generated, the expansion quantity is absorbed by the expansion joint of the movable end, so that the multistage combined sealing structure 4 and the pre-sealing structure 2 can operate effectively, and the sealing stability is ensured.

There are two seal structures between the device shell and the rotary shaft, the first seal structure is a pre-seal structure 2 connected with the device shell, and the first seal structure is static when the rotary shaft works, so that a static seal structure is formed, and most of high-temperature gas in the device is blocked at the pre-seal structure 2 by the multistage seal structure at the position. The second sealing structure is a multi-stage combined sealing structure 4 arranged between the expansion joint and the bearing, and rotates along with the expansion joint and the bearing when the rotary shaft works to form a dynamic sealing structure, and the multi-stage combined sealing structure 4 further seals overflowed gas at the pre-sealing structure 2 to form a double-insurance second sealing structure.

The foregoing detailed description has been provided for the purposes of illustration in connection with specific embodiments and exemplary examples, but such description is not to be construed as limiting the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications and improvements may be made to the technical solution of the present application and its embodiments without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The scope of the application is defined by the appended claims.

What is not described in detail in the present specification is a well known technology to those skilled in the art.

Claims (10)

1. The utility model provides a multistage combination revolving shaft sealing device that can self-adaptation is centered which characterized in that: comprises a fixed end and a sliding end which are connected with two ends of a rotating shaft (7), wherein the fixed end and the sliding end are both connected between a device shell (6) and the rotating shaft (7);

the sliding end comprises a pre-sealing structure (2), an expansion joint (3), a multi-stage combined sealing structure (4) and a self-supporting bearing assembly (5) which are sequentially connected along the axis of a rotating shaft (7), wherein the pre-sealing structure (2), the expansion joint (3), the multi-stage combined sealing structure (4) and the self-supporting bearing assembly (5) are all sleeved outside the rotating shaft (7), one side, deviating from the expansion joint (3), of the pre-sealing structure (2) is connected with an equipment shell (6), the rotating shaft (7) is externally fixed with a shaft sleeve (5-2), the self-supporting bearing assembly (5) comprises a self-aligning roller bearing (5-3) and a positioning shell, the inner ring of the self-aligning roller bearing (5-3) is connected with the shaft sleeve (5-2), the outer ring is connected with the positioning shell, the positioning shell is connected with the multi-stage combined sealing structure (4), and the expansion joint (3) is of a flexible structure.

2. The self-adaptive centering multi-stage combined rotary shaft sealing device according to claim 1, wherein: the sliding end further comprises a positioning chuck structure (1), the positioning chuck structure (1) is connected between the equipment shell (6) and the pre-sealing structure (2), and the positioning chuck structure (1) is coaxial with the rotating shaft (7) when being tightened.

3. The self-aligning multi-stage combined rotary shaft sealing device according to claim 2, wherein: the pre-sealing structure (2) comprises a pre-sealing ring and a multi-stage static sealing structure connected to the inner side of the pre-sealing ring, the multi-stage static sealing structure is in contact with the outer wall of the rotary shaft (7), and the pre-sealing ring is fixedly connected with the positioning chuck structure (1).

4. The self-adaptive centering multi-stage combined rotary shaft sealing device according to claim 1, wherein: the expansion joint (3) comprises a corrugated pipe (3-3), an inner end flange (3-1) and an outer end flange (3-2), wherein the inner end flange (3-1) and the outer end flange (3-2) are connected to two ends of the corrugated pipe, the inner end flange (3-1) is fixedly connected to the pre-sealing structure (2), and the outer end flange (3-2) is fixedly connected to the multi-stage combined sealing structure (4).

5. The self-adaptive centering multi-stage combined rotary shaft sealing device according to claim 1, wherein: the multistage combined sealing structure (4) comprises a fixed sleeve and a dynamic sealing structure, the fixed sleeve is sleeved on the outer side of the shaft sleeve (5-2), the dynamic sealing structure is connected between the fixed sleeve and the shaft sleeve (5-2), and the fixed sleeve is fixedly connected between the expansion joint (3) and the positioning shell.

6. The self-adaptive centering multi-stage combined rotary shaft sealing device according to claim 5, wherein: the positioning shell comprises a bearing cover (5-1) and a bearing seat cover (5-5) which are fixedly connected, the bearing cover (5-1) is fixedly connected with the expansion joint (3) and the fixing sleeve, the bearing cover (5-1) and the bearing seat cover (5-5) are sleeved on the outer side of the bearing, and a gap is reserved between one end of the inner side of the bearing cover (5-1) and the end face of the outer ring of the bearing (5-3) so as to enable the bearing (5-3) to be slidably positioned.

7. The self-adaptive centering multi-stage combined rotary shaft sealing device of claim 6, wherein: a cavity is formed between the two end faces of the bearing (5-3) and the positioning shell, and a sealing structure is arranged between the shaft sleeve (5-2) and the positioning shell so as to isolate the inner cavity of the positioning shell from the outside.

8. The self-adaptive centering multi-stage combined rotary shaft sealing device of claim 7, wherein: the sealing structure comprises two bearing part sealing rings (5-4), wherein one bearing part sealing ring (5-4) is used for sealing and fixing a gap between the sleeve and the shaft sleeve (5-2), and the other bearing part sealing ring (5-4) is used for sealing a gap between the shaft sleeve (5-2) and the bearing seat cover (5-5), so that cavities at two ends of the bearing (5-3) are isolated from the outside.

9. The self-aligning multi-stage combined rotary shaft sealing device according to claim 8, wherein: the bearing housing is provided with an isolation gas inlet (5-6), one end of the isolation gas inlet (5-6) is communicated with the cavities at two ends of the bearing (5-3), and the other end of the isolation gas inlet is communicated with the outer wall of the bearing housing (5-1) and is connected with an isolation gas source.

10. The self-adaptive centering multi-stage combined rotary shaft sealing device according to claim 1, wherein: the fixed end comprises a positioning chuck structure, a pre-sealing structure, a multi-stage combined sealing structure and a self-supporting bearing assembly which are sequentially and fixedly connected along the axis of the rotary shaft, wherein the positioning chuck structure, the pre-sealing structure, the multi-stage combined sealing structure and the self-supporting bearing assembly are all sleeved outside the rotary shaft, a shaft sleeve is fixedly arranged outside the rotary shaft, the self-supporting bearing assembly comprises a self-aligning roller bearing and a positioning shell, the inner ring of the self-aligning roller bearing is connected with the shaft sleeve, the outer ring of the self-aligning roller bearing is connected with the positioning shell, and the positioning shell is connected with the multi-stage combined sealing structure.