CN218023793U

CN218023793U - Rolling element with sealed cavity

Info

Publication number: CN218023793U
Application number: CN202220897911.9U
Authority: CN
Inventors: 张晓峰; 马兰英; 亓鹏
Original assignee: Shandong Lingxiyuan Technology Development Co ltd
Current assignee: Shandong Lingxiyuan Technology Development Co ltd
Priority date: 2022-04-18
Filing date: 2022-04-18
Publication date: 2022-12-13
Anticipated expiration: 2032-04-18

Abstract

The application discloses a rolling body with a sealed cavity, which comprises a shell, an outer cover, a ball, a middle cover and an elastic wear-resistant part, wherein a mounting groove is formed in the shell, and a supporting surface is formed on the inner wall of the shell; the outer cover covers the opening of the mounting groove, a mounting cavity is formed by the outer cover and the inner wall of the mounting groove in a surrounding mode, and the outer cover is provided with a mounting hole; the ball is arranged in the mounting cavity, the support surface supports the ball, and part of the ball extends out of the shell through the mounting hole; the middle cover is arranged in the mounting groove and is provided with a through hole, part of the ball passes through the through hole to be supported with the supporting surface, and the middle cover and the outer cover surround the ball to form a sealing cavity; the elastic wear-resistant part is arranged in the sealing cavity and is abutted against the ball. The sealed chamber of this rolling element is enclosed by a plurality of part combinations, avoids making the chamber of placing the elasticity wearing parts alone in the mounting groove, the manufacturing of being convenient for to be convenient for when the ball rolls, effectively clear away the impurity of attaching to on the ball, avoid inside impurity gets into the shell, and then influence the normal work of ball.

Description

Rolling element with sealed cavity

Technical Field

The utility model relates to a material field of carrying especially relates to a rolling element with sealed chamber.

Background

At present, the existing rolling element generally comprises a shell and a ball, wherein the shell forms a mounting cavity, the ball is mounted in the mounting cavity, and part of the ball extends out of the bottom side of the shell and can roll in the mounting cavity. The rolling element can be used for material conveyor to reduce the resistance of material conveyor operation, for example the rolling element can be applied to scraper conveyor, scraper conveyor is the conveyor of transport coal and material, includes the chain and installs the scraper blade on the chain usually, and the chain can drive the scraper blade and slide along the chute. However, the scraper conveyor is usually used in a coal mine and other scenes with poor environmental cleanliness, and the chute usually contains impurities such as coal dust, sludge and the like. The scraper blade is at the operation in-process, and impurity piles up in the running resistance that the impurity that installs the intracavity can increase the ball in the shell of rolling element easily, makes the ball card even in the installation intracavity and be difficult to rotate.

SUMMERY OF THE UTILITY MODEL

In order to solve the problem, the utility model provides a rolling element with sealed chamber, the sealed chamber of this rolling element is enclosed by a plurality of part combinations, avoids the chamber of placing elasticity wearing parts alone in the preparation of mounting groove, and the manufacturing of being convenient for to be convenient for when the ball rolls, effectively clear away the impurity of adhering to on the ball, avoid inside impurity gets into the shell, and then influence the normal work of ball.

In order to achieve the purpose, the utility model provides a rolling element with a sealed cavity, which comprises a shell, an outer cover, a ball, a middle cover and an elastic wear-resistant part, wherein the interior of the shell is provided with a mounting groove, and the inner wall of the shell is provided with a supporting surface; the outer cover covers the opening of the mounting groove, a mounting cavity is formed by the outer cover and the inner wall of the mounting groove in a surrounding mode, and the outer cover is provided with a mounting hole; the ball is arranged in the mounting cavity, the support surface supports the ball, and part of the ball extends out of the shell through the mounting hole; the middle cover is arranged in the mounting groove and provided with a through hole, part of the ball passes through the through hole to be supported with the supporting surface, and the middle cover and the outer cover surround the ball to form a sealing cavity; the elastic wear-resistant part is arranged in the sealing cavity and is abutted against the ball.

Further, the edge of the bottom end of the outer cover extends inwards to form a first annular rib, the first annular rib extends inwards to be close to the balls to form an opening, and the opening forms the mounting hole.

Furthermore, the edge of well lid one end inwards extends and forms the second ring muscle, and the second ring muscle inwards extends to and forms the opening near the ball, and the opening forms the through-hole, and first ring muscle, second ring muscle and ball surface enclose into the seal chamber.

Further, the second ring rib is located on the upper side of the center of the ball.

Furthermore, the middle cover is in transition fit connection with the inner wall of the mounting groove.

Further, the enclosing cover is equipped with helicitic texture including connecting the boss, the connection boss outside, and the lateral wall of mounting groove is corresponding to be equipped with the screw hole section, connects boss and well lid butt.

Further, elasticity wearing parts is equipped with the butt side including sealed wear ring, and the butt side is laminated the butt with the ball surface mutually, and the butt side is opened and is equipped with a plurality of annular grooves.

Furthermore, the sealing wear-resisting ring is provided with a separating part extending into the mounting hole, the separating part extends outwards to be flush with the outer end face of the outer cover, and the separating part separates the ball and the hole wall of the mounting hole at the mounting hole.

Furthermore, the elastic wear-resistant piece also comprises a fastening ring, and the fastening ring is sleeved on the sealing wear-resistant ring.

Furthermore, the inner wall of the outer cover close to the rolling balls is of an arc-shaped structure, so that the inner wall of the outer cover is abutted to the fastening ring.

The beneficial effects of the utility model reside in that, the sealed chamber of this rolling element is enclosed by a plurality of part combinations, avoids making the chamber of placing elasticity wearing parts alone in the mounting groove, and the manufacturing of being convenient for to be convenient for when the ball rolls, effectively clear away the impurity of adhering to on the ball, avoid impurity to get into inside the shell, and then influence the normal work of ball.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the application and not to limit the invention. In the drawings:

FIG. 1 is a schematic structural view of a rolling element according to an embodiment of the present invention;

fig. 2 is a sectional view of the roller body in the embodiment shown in fig. 1.

Wherein: 10. a housing; 101, mounting a groove; 1011. a threaded segment; 102. a support surface; 11. an outer cover; 111. mounting holes; 112. a first annular rib; 113. connecting the bosses; 12. a ball bearing; 13. a middle cover; 131. a through hole; 132. a second annular rib; 14. an elastic wear member; 141. sealing a wear-resistant ring; 1411. an abutment side; 1412. an annular groove; 1413. a partition portion; 142. a fastening ring; 20. sealing the cavity; 30. and (5) small balls.

Detailed Description

In order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example in conjunction with the accompanying drawings.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and therefore the scope of the present invention is not limited by the specific embodiments disclosed below.

In addition, in the description of the present invention, it is to be understood that the terms "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present invention and to simplify the description, and do not indicate or imply that the device or element so referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," and "fixed" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally formed; the connection can be mechanical connection, electrical connection or communication; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present application, unless expressly stated or limited otherwise, a first feature "on" or "under" a second feature may be directly contacting the second feature or the first and second features may be indirectly contacting the second feature through intervening media. In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

In the present invention, as shown in fig. 1 to 2, a rolling element with a sealed cavity 20 is provided, which includes a housing 10, an outer cover 11, a ball 12, a middle cover 13, and an elastic wear-resistant member 14, wherein a mounting groove 101 is provided inside the housing 10, and a supporting surface 102 is formed on an inner wall of the housing 10; the outer cover 11 covers the opening of the mounting groove 101, the outer cover 11 and the inner wall of the mounting groove 101 enclose a mounting cavity, and the outer cover 11 is provided with a mounting hole 111; the ball 12 is arranged in the mounting cavity, the supporting surface 102 supports the ball 12, and part of the ball 12 extends out of the housing 10 through the mounting hole 111; the middle cover 13 is arranged in the mounting groove 101, the middle cover 13 is provided with a through hole 131, the ball 12 penetrates through the through hole 131 to be supported with the supporting surface 102, and the middle cover 13 and the outer cover 11 surround the ball 12 to form a sealing cavity 20; the resilient wear member 14 is disposed in the seal cavity 20, and the resilient wear member 14 abuts the ball 12.

In a scraper conveyor, rolling elements are mounted at the bottom of the scraper conveyor such that balls 12 of the rolling elements extending out of a housing 10 come into contact with a chute of the scraper conveyor, by rolling of the balls 12 on the chute, the running resistance of the material conveying device is reduced. In the above structure, the balls 12 are placed in the mounting groove 101 in the housing 10, the outer cover 11 covers the opening of the mounting groove 101, and part of the balls 12 extend out of the housing 10 through the mounting holes 111 on the outer cover 11, so as to realize the rolling of the balls 12, the balls 12 can be effectively prevented from falling off from the housing 10 during the operation by using the outer cover 11, and in addition, the supporting surface 102 is formed on the inner wall of the mounting groove 101, so that the housing 10 can provide enough supporting function for the balls 12 when the balls 12 roll.

As shown in fig. 1 and 2, a middle cover 13 is further arranged in the mounting groove 101, a through hole 131 for the ball 12 to pass through is formed in the middle cover 13, after the middle cover 13 is mounted, a sealing cavity 20 surrounding the ball 12 is defined by the outer surfaces of the middle cover 13, the upper cover and the ball 12, and the elastic wear-resistant piece 14 is placed in the sealing cavity 20, so that the elastic wear-resistant piece 14 is abutted to the ball 12. Because the part of the ball 12 extending out of the casing 10 is in contact with the chute, impurities are easy to attach, and the impurities are easy to enter the mounting groove 101 along with the ball 12 in the rolling process of the ball 12, so that the rolling resistance of the ball 12 in the mounting groove 101 is easy to increase, and the rolling of the ball 12 is further influenced. The seal cavity 20 is provided with an elastic wear-resistant piece 14, and the elastic wear-resistant piece 14 is abutted against the ball 12, so that the elastic wear-resistant piece 14 can scrape impurities adhered to the ball 12 during the rolling process of the ball 12 to reduce the impurities from entering the mounting groove 101.

The sealing cavity 20 formed by enclosing the middle cover 13, the outer cover 11 and the balls 12 is convenient to form, a cavity for separately placing the elastic wear-resistant part 14 is avoided being manufactured in the mounting groove 101, production and manufacturing are convenient, in addition, the sealing cavity 20 is convenient for mounting and dismounting the elastic wear-resistant part 14, and during mounting or dismounting, the elastic wear-resistant part 14 can be placed in or taken out only by opening the outer cover 11, so that operation is convenient; in addition, the outer cover 11 and the middle cover 13 are arranged, so that the balls 12 pass through the through holes 131 and the mounting holes 111, the positions of the balls 12 are further limited, the phenomenon that the balls 12 are deviated in the rolling process is avoided, and the rolling stability of the balls 12 is improved.

Since the balls 12 continuously rub against the elastic wear-resistant member 14 during rolling, the elastic wear-resistant member 14 may be made of a material with good wear resistance, such as a wear-resistant ring made of polytetrafluoroethylene, polyimide, polyamideimide, or polyetheretherketone. In addition, the elastic wear-resistant pieces 14 have elasticity, so that the balls 12 can play a role in vibration reduction to a certain extent when rolling. In particular, the balls 12 have random circumferential rotation during rolling, and after some impurities enter between the balls 12 and the elastic wear-resistant pieces 14, when the impact force of the balls 12 towards the impurities is large, due to the effect of elastic vibration reduction, the direct extrusion force of the balls 12 to the impurities is reduced, and the abrasion of the balls 30 can be reduced. When the impact force of the balls 12 in the opposite direction to the foreign matter is large, the pressure of the balls 12 to the foreign matter is reduced due to the elastic damping effect of the elastic abrasion resistant member 14, and the abrasion of the balls 30 can be reduced.

In one embodiment, as shown in FIG. 2, a plurality of small balls 30 are disposed between the ball 12 and the support surface 102 such that the ball 12 contacts the small balls 30 during rolling, further reducing the resistance of the support surface 102 to the ball 12 and also facilitating the rolling of the ball 12.

In a preferred embodiment, as shown in fig. 2, the edge of the bottom end of the outer cover 11 extends inward to form a first annular rib 112, the first annular rib 112 extends inward to form an opening adjacent to the ball 12, and the opening forms the mounting hole 111. The bottom end edge of the outer cover 11 extends inwards to form a first annular rib 112, the opening of the first annular rib 112 is closed, and part of the balls 12 extend out of the outer shell 10 through the mounting holes 111 on the first annular rib 112, so that the balls 12 can roll in the chute, and meanwhile, the rollers can be prevented from falling off from the mounting grooves 101, and the normal work of the rolling bodies is influenced. In addition, the arrangement of the first annular rib 112 can further reduce the space occupied by the outer cover 11 in the mounting groove 101, so that the installation space of the elastic wear-resistant part 14 is relatively increased, and the installation of the elastic wear-resistant part 14 is facilitated.

More specifically, as shown in fig. 2, an edge of one end of the middle cap 13 extends inward to form a second annular rib 132, the second annular rib 132 extends inward to form an opening close to the balls 12, the opening forms a through hole 131, and the first annular rib 112, the second annular rib 132 and the outer surface of the balls 12 define the sealed cavity 20. The second ring muscle 132 that well lid 13 formed arranges first ring muscle 112 upside on the enclosing cover 11 in, thereby second ring muscle 132 and first ring muscle 112 form the upper and lower both ends of seal chamber 20, thereby further restrict reciprocating of elasticity wearing parts 14 through first ring muscle 112 and second ring muscle 132, avoid elasticity wearing parts 14 to drop or the dislocation at work, thereby influence the sealed ability of scraping impurity of elasticity wearing parts 14, and then improve sealed stability.

In one embodiment, the outer cover 11 extends upward to the middle cover 13, such that the first annular rib 112, the inner wall of the outer cover 11, the second annular rib 132 and the outer surface of the ball 12 enclose the sealed cavity 20, while in another alternative embodiment, the middle cover 13 extends downward to the outer cover 11, such that the first annular rib 112, the second annular rib 132, the inner wall of the middle cover 13 and the outer surface of the ball 12 enclose the sealed cavity 20.

In a preferred embodiment, the second annular rib 132 is located on the upper side of the centre of the ball 12 as shown in figure 2.

In the above structure, the second ring rib 132 on the middle cover 13 is installed on the upper side of the center of the ball 12, thereby facilitating the installation of the middle cover 13, when the middle cover 13 is installed, the middle cover 13 can be placed in the installation groove 101 first, then the ball 12 is installed, since the ball 12 needs to be maintained periodically, therefore, the middle cover 13 is installed first, thereby facilitating the installation and disassembly of the ball 12, and meanwhile, when the middle cover 13 is installed on the ball 12 in advance, then the ball 12 is installed in the installation groove 101, thereby simplifying the installation steps. In addition, a part of the balls 12 are supported with the supporting surface 102 through the through holes 131 on the middle cover 13, the middle cover 13 is installed on the upper side of the center of the ball 12, and the upward movement of the ball 12 can be further limited, so that the friction of the ball 12 against the supporting surface 102 is increased, the rolling resistance of the ball 12 in the mounting groove 101 is improved, in addition, the abrasion of the supporting surface 102 is accelerated, and the service life of the supporting surface 102 is shortened.

In a preferred embodiment, as shown in fig. 2, the middle cover 13 is in transition fit connection with the inner wall of the installation groove 101. When lid 13 in the installation, with well lid 13 and the installation of mounting groove 101 inner wall transition fit, the installation and the dismantlement of being convenient for also avoid setting up the screw hole in mounting groove 101, have guaranteed mounting groove 101's an organic whole nature, have improved well lid 13's installation effectiveness.

More specifically, as shown in fig. 2, the outer cover 11 includes a connecting boss 113, a thread structure is disposed on an outer side of the connecting boss 113, a threaded hole section 1011 is correspondingly disposed on a side wall of the mounting groove 101, and the connecting boss 113 abuts against the middle cover 13.

To the fixed mode of enclosing cover 11 and shell 10 on, set up connection boss 113 on the enclosing cover 11, place connection boss 113 in mounting groove 101, the connection boss 113 outside sets up the helicitic texture, simultaneously, be equipped with screw section 1011 in mounting groove 101, the helicitic texture and the screw section 1011 through connecting the boss 113 outside are connected through screw-thread fit, the joint strength of enclosing cover 11 and shell 10 has been improved, because ball 12 rolls in mounting groove 101 in work, can produce great effect to enclosing cover 11, in addition, enclosing cover 11 bears ball 12's action of gravity simultaneously, very easily because of the effect of force in the separation of shell 10, thereby reduce the restriction to ball 12, ball 12 drops in easy follow mounting groove 101, influence its normal work.

In addition, the connecting boss 113 on the outer cover 11 abuts against the middle cover 13, so that the middle cover 13 is fastened, and the phenomenon that the middle cover 13 loosens and falls off is avoided, and the sealing effect is influenced.

In a preferred embodiment, as shown in fig. 2, the elastic wear-resistant member 14 includes a seal wear-resistant ring 141, the seal wear-resistant ring 141 is provided with an abutting side 1411, the abutting side 1411 abuts against the outer surface of the ball 12, and the abutting side 1411 is provided with a plurality of annular grooves 1412.

The elastic wear-resistant piece 14 comprises a sealing wear-resistant ring 141, the part of the sealing wear-resistant ring 141 abutted against the outer side face of the ball 12 forms an abutting side 1411, the abutting side 1411 can be an arc abutting side 1411 consistent with the arc of the outer side face of the ball 12, the sealing wear-resistant ring 141 can be better attached to the ball 12, impurities attached to the ball 12 can be better scraped in the rolling process of the ball 12, the impurities are reduced from entering the mounting groove 101, the ball 12 and the inner wall of the mounting groove 101 are damaged, and the ball 12 is extremely easily prevented from rolling in the mounting groove 101. In addition, the abutting side 1411 is provided with a plurality of annular grooves 1412, so that a certain gap exists between the ball 12 and the seal wear-resistant member, the friction force of the seal wear-resistant member on the ball 12 is reduced, and the seal wear-resistant ring 141 is prevented from influencing the rolling of the ball 12.

More specifically, as shown in fig. 2, the seal wear ring 141 has a partition portion 1413 that extends into the mounting hole 111, the partition portion 1413 extends outward to be flush with the outer end surface of the outer cover 11, and the partition portion 1413 partitions the balls 12 and the hole wall of the mounting hole 111 at the mounting hole 111.

In the above configuration, the partition 1413 can restrain the ball 12 in the lateral direction, prevent the ball 12 from directly impacting the hole wall of the mounting hole 111 during rolling, and cushion the impact force of the ball 12 against the housing 10. Moreover, when the ball 12 rotates in the mounting hole 111, the partition 1413 prevents the ball 12 from directly rubbing against the hole wall of the mounting hole 111, and reduces wear of the hole wall of the mounting hole 111. In addition, impurities are easily adhered to the outer surface of the ball 12 during the rolling process, and when the ball 12 rolls, the partition 1413 can scrape the impurities on the outer surface of the ball 12, reduce the occurrence of blockage at the mounting hole 111, and reduce the impurities brought into the mounting groove 101 by the ball 12.

Further, as shown in fig. 2, the elastic wear-resistant member 14 further includes a fastening ring 142, and the fastening ring 142 is disposed on the sealing wear-resistant ring 141. In the rolling process of the ball 12, the seal wear-resistant ring 141 and the ball 12 continuously rub against each other, and after long-term use, the seal wear-resistant ring 141 is worn to a certain extent, so that a gap exists between the seal wear-resistant ring 141 and the ball 12. The fastening ring 142 can apply pressure to the seal wear ring 141 through elastic deformation, and press the seal wear ring 141 against the outer surface of the ball 12, so as to compensate the force of the seal wear ring 141, reduce the gap between the seal wear ring 141 and the ball 12, improve the sealing performance, and prolong the service life thereof.

In one embodiment, as shown in fig. 2, the fastening ring 142 is a plurality of O-rings fitted over the seal wear ring 141.

More specifically, as shown in fig. 2, the inner wall of the cover 11 adjacent to the balls 12 has an arc-shaped structure, so that the inner wall of the cover 11 abuts against the fastening ring 142.

The inner wall of the outer cover 11 close to the fastening ring 142 is designed to be of an arc-shaped structure, so that the inner wall is abutted to the fastening ring 142, the force applied to the fastening ring 142 is increased, the fastening effect of the fastening ring 142 and the sealing wear-resistant ring 141 is facilitated, and the stability of the fastening ring 142 is improved.

In a further alternative embodiment, the inner wall of the outer cap 11 adjacent to the fastening ring 142 has a stepped structure, so that the fastening ring 142 is better abutted against the inner wall of the outer cap 11, thereby providing a better restraining force to the fastening ring 142.

The utility model can be realized by adopting or using the prior art for reference in places which are not mentioned in the utility model.

The above description is only an example of the present invention and is not intended to limit the present invention. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A rolling element having a sealed cavity, comprising:

the mounting groove is formed in the shell, and a supporting surface is formed on the inner wall of the shell;

the outer cover covers the opening of the mounting groove, a mounting cavity is defined by the outer cover and the inner wall of the mounting groove, and the outer cover is provided with a mounting hole;

the ball bearing is arranged in the mounting cavity, the supporting surface supports the ball bearing, and part of the ball bearing extends out of the shell through the mounting hole;

the middle cover is arranged in the mounting groove and provided with a through hole, part of the ball passes through the through hole and is supported by the supporting surface, and the middle cover and the outer cover surround the ball to form a sealed cavity;

the elastic wear-resistant part is arranged in the sealing cavity and is abutted to the ball.

2. The rolling element with a sealed cavity according to claim 1, wherein: the edge of the bottom end of the outer cover extends inwards to form a first annular rib, the first annular rib extends inwards to be close to the ball to form an opening, and the opening forms the mounting hole.

3. The rolling element with a sealed cavity according to claim 2, wherein: the edge of one end of the middle cover extends inwards to form a second annular rib, the second annular rib extends inwards to be close to the ball to form an opening, the opening forms the through hole, and the first annular rib, the second annular rib and the outer surface of the ball are enclosed to form the sealing cavity.

4. The rolling element with a sealed cavity according to claim 3, wherein: the second annular rib is positioned on the upper side of the sphere center of the ball.

5. The rolling element with a sealed cavity according to claim 1, wherein: the middle cover is in transition fit connection with the inner wall of the mounting groove.

6. The rolling element with a sealed cavity according to claim 5, wherein: the enclosing cover is including connecting the boss, it is equipped with helicitic texture to connect the boss outside, the lateral wall of mounting groove is corresponding to be equipped with the screw hole section, connect the boss with well lid butt.

7. The rolling element with a sealed cavity according to claim 1, wherein: the elastic wear-resistant part comprises a sealing wear-resistant ring, the sealing wear-resistant ring is provided with a butt side, the butt side is abutted to the outer surface of the ball, and a plurality of annular grooves are formed in the butt side.

8. The rolling element with sealed cavities of claim 7, wherein: the sealing wear-resisting ring is provided with a separating part extending into the mounting hole, the separating part extends outwards to be flush with the outer end face of the outer cover, and the separating part separates the ball and the hole wall of the mounting hole at the mounting hole.

9. The rolling element with a sealed cavity according to claim 7, wherein: the elastic wear-resistant piece further comprises a fastening ring, and the fastening ring is sleeved on the sealing wear-resistant ring.

10. The rolling element with sealed cavities of claim 9, wherein: the inner wall of the outer cover close to the ball is of an arc-shaped structure, so that the inner wall of the outer cover is in annular butt joint with the fastening ring.