A tire expansion assembly and internal support tooling
By designing an expansion assembly and utilizing the cooperation of a threaded sleeve and an expansion ring, stable support and position adjustment of thin-walled cylindrical parts can be achieved, solving the problem of easy damage or detachment of thin-walled cylindrical parts during processing and improving processing accuracy and safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SICHUAN RUNBO ZHIYUAN TECH CO LTD
- Filing Date
- 2025-06-17
- Publication Date
- 2026-05-26
AI Technical Summary
Thin-walled cylindrical parts are difficult to fix during processing, and ordinary clamps are prone to damage or detachment, leading to processing hazards.
Design an expansion tire assembly including a mounting base, a first threaded sleeve, a second threaded sleeve, and multiple expansion rings. The rotation of the first threaded sleeve drives the second threaded sleeve to move axially, which in turn pushes the expansion rings to move radially. The arc-shaped support surface stably supports the inner wall of the thin-walled cylindrical component, and the position of the expansion rings can be adjusted to accommodate different sizes.
It achieves stable support for thin-walled cylindrical parts, avoids deformation and clamping damage, and improves machining accuracy and safety.
Smart Images
Figure CN224274131U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of cylindrical component processing technology, specifically relating to a tire expansion assembly and an internal support tooling. Background Technology
[0002] Thin-walled cylindrical parts are a common occurrence in machining. However, due to the small wall thickness of the workpiece, it is difficult to fix it with ordinary fixtures during machining. On the one hand, it is easy to damage the workpiece, and on the other hand, the thin wall thickness makes it difficult to clamp with ordinary fixtures, and the workpiece is easy to fall off during machining, which may cause danger. Utility Model Content
[0003] The purpose of this application is to provide a tire expansion component and an internal support tooling to solve the aforementioned technical problems existing in the prior art.
[0004] This application is implemented as follows:
[0005] In a first aspect, embodiments of this application provide a tire expansion assembly, including a mounting base, a first threaded sleeve, a second threaded sleeve, and multiple expansion rings. The mounting base is an annular structure and is coaxially arranged with the first and second threaded sleeves. The first threaded sleeve is rotatably mounted on the mounting base and is axially positioned within the mounting base. The second threaded sleeve is threaded onto the outside of the first threaded sleeve, and its outer peripheral wall includes multiple first mating surfaces distributed circumferentially. The expansion rings are radially movably connected to the mounting base along the second threaded sleeve. One end of the expansion ring has an arc-shaped support surface, and the other end has a second mating surface that contacts the first mating surface. The expansion rings correspond one-to-one with the first mating surfaces, and at least one of the first and second mating surfaces is inclined relative to the axis of the second threaded sleeve. The first threaded sleeve can rotate under external force to drive the second threaded sleeve to move axially, thereby pushing the expansion rings to move radially along the second threaded sleeve.
[0006] Secondly, this application provides an internal support tooling, including an internal support tube and a plurality of expansion tire components provided in the first aspect embodiment. The plurality of expansion tire components are distributed along the axial direction of the internal support tube. The mounting base is installed on the internal support tube and is coaxially arranged with the internal support tube. The inner diameter of the first threaded sleeve is smaller than the inner diameter of the internal support tube.
[0007] The technical solution provided in this application can achieve the following beneficial effects:
[0008] In this application, an arc-shaped support surface is provided at one end of the expansion ring. The arc-shaped support surface supports the inner wall of the thin-walled cylindrical part to be processed, providing stable support for the thin-walled cylindrical part. The position of the thin-walled cylindrical part is stabilized by stabilizing the position of the expansion ring, which facilitates the processing of the thin-walled cylindrical part and avoids deformation or collapse during processing. It also avoids damage to the thin-walled cylindrical part by directly clamping it. At the same time, this application provides a first threaded sleeve and a second threaded sleeve in cooperation. Rotating the first threaded sleeve drives the second threaded sleeve to move along its axial direction. Through the cooperation between the second threaded sleeve and the expansion ring, the movement of the second threaded sleeve along its axial direction drives the expansion ring to move radially along the second threaded sleeve, adjusting the position of the expansion ring. This adjusts the overall radial dimension of the expansion tire assembly, making it easier to place the expansion tire assembly inside the thin-walled cylindrical part, so that the arc-shaped support surface of the expansion ring can support the inner wall of the thin-walled cylindrical part. Attached Figure Description
[0009] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0010] Figure 1 This is a schematic diagram of the overall structure of the tire expansion assembly provided in some embodiments of this application;
[0011] Figure 2 This application is about Figure 1 AA section view;
[0012] Figure 3 This is a partial cross-sectional view of a tire expansion assembly provided in some embodiments of this application;
[0013] Figure 4 This is a schematic diagram of the fit between the first threaded sleeve, the second threaded sleeve, and the expansion ring provided in some embodiments of this application;
[0014] Figure 5 This is a cross-sectional view of the tire expansion assembly provided in some embodiments of this application;
[0015] Figure 6 This is a schematic diagram of the overall structure of the internal support tooling provided in some embodiments of this application.
[0016] In the diagram: 100-mounting base, 200-first threaded sleeve, 300-second threaded sleeve, 310-first mating surface, 400-expansion ring, 410-arc-shaped support surface, 420-second mating surface, 430-mounting groove, 500-compression spring, 600-expansion ring stop pin, 700-inner support tube, 800-end cap, 900-part to be supported. Detailed Implementation
[0017] The following description provides many different embodiments or examples for implementing various features of the present invention. The elements and arrangements described in the specific examples below are only for concise expression of the present invention and are merely examples, not intended to limit the present invention.
[0018] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.
[0019] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more.
[0020] This application provides a tire expansion assembly, which can be referred to as [reference needed]. Figures 1 to 3 As shown, the tire expansion assembly includes a mounting base 100, a first threaded sleeve 200, a second threaded sleeve 300, and multiple expansion rings 400.
[0021] The mounting base 100 has a ring structure, and the mounting base 100, the first threaded sleeve 200, and the second threaded sleeve 300 are coaxially arranged.
[0022] The first threaded sleeve 200 is rotatably mounted on the mounting base 100. The first threaded sleeve 200 can rotate relative to the mounting base 100, and at the same time, the first threaded sleeve 200 is axially limited and engaged with the mounting base 100. Due to the limitation of the mounting base 100, the axial position of the first threaded sleeve 200 can remain stable and will not move when rotating.
[0023] The second threaded sleeve 300 is threaded onto the outside of the first threaded sleeve 200. The second threaded sleeve 300 has an internal thread, and the first threaded sleeve 200 has an external thread. The two are threadedly connected, and the outer peripheral wall of the second threaded sleeve 300 includes a plurality of first mating surfaces 310 distributed circumferentially thereon. The outer peripheral surface of the second threaded sleeve 300 is its peripheral sidewall away from the first threaded sleeve 200, and this peripheral sidewall has a plurality of first mating surfaces 310.
[0024] An expansion ring 400 is movably connected to the mounting base 100 along the radial direction of the second threaded sleeve 300, and the expansion ring 400 can move relative to the mounting base 100 along the radial direction of the second threaded sleeve 300. One end of the expansion ring 400 is provided with an arc-shaped support surface 410, which is used to contact the inner wall of the thin-walled cylindrical part to be processed, supporting the thin-walled cylindrical part. The other end of the expansion ring 400 is provided with a second mating surface 420 that contacts the first mating surface 310. The expansion rings 400 and the first mating surfaces 310 are arranged in a one-to-one correspondence, with one first mating surface 310 corresponding to one expansion ring 400. Similar to the arrangement of multiple first mating surfaces 310, multiple expansion rings 400 are also distributed along the circumference of the second threaded sleeve 300. Furthermore, at least one of the first mating surface 310 and the second mating surface 420 is inclined relative to the axis of the second threaded sleeve 300.
[0025] The first threaded sleeve 200 can rotate under the action of external force to drive the second threaded sleeve 300 to move along its axial direction. The movement of the second threaded sleeve 300 along its axial direction can push the expansion ring 400 to move radially along the second threaded sleeve 300, thereby adjusting the position of the expansion ring 400 so that the arc-shaped support surface 410 of the expansion ring 400 can support the inner wall of the corresponding thin-walled cylindrical part.
[0026] The arc-shaped support surface 410 is arc-shaped, and the multiple arc-shaped support surfaces 410 of the expansion rings 400 together support the inner wall of the thin-walled cylindrical part, which can stabilize the position of the thin-walled cylindrical part. The position of the thin-walled cylindrical part can be fixed by fixing the position of the expansion assembly, which facilitates the processing of the thin-walled cylindrical part. Using the arc-shaped support surface 410 to fix the position of the thin-walled cylindrical part instead of a clamp avoids clamping the thin-walled cylindrical part and avoids clamping damage to the thin-walled cylindrical part.
[0027] The second threaded sleeve 300 needs to be circumferentially fitted with the mounting base 100, preventing it from rotating relative to the mounting base 100. Thus, when the first threaded sleeve 200 is rotated, the second threaded sleeve 300 can be driven to move axially, converting the rotational motion of the first threaded sleeve 200 into linear motion. The expansion ring 400, however, is limited by the mounting base 100 and can only move radially along it. Therefore, as the second threaded sleeve 300 moves axially, the contact position between the second mating surface 420 and the first mating surface 310 changes. Since at least one of the first mating surface 310 and the second mating surface 420 is inclined relative to the axis of the second threaded sleeve 300, the distance between the inclined surface and the axis of the second threaded sleeve 300 gradually decreases or increases along the axial direction of the second threaded sleeve 300. As the contact position of the first mating surface 310 and the second mating surface 420 changes, the second threaded sleeve 300 can push the expansion ring 400 to move radially along the second threaded sleeve 300, thereby adjusting the position of the expansion ring 400.
[0028] Adjusting the expansion ring 400 to a position close to the second threaded sleeve 300 reduces the overall radial dimension of the expansion assembly, facilitating its placement within or removal from the thin-walled cylinder. Adjusting the expansion ring 400 to a position away from the second threaded sleeve 300 increases the overall radial dimension of the expansion assembly, allowing the arc-shaped support surface 410 of the expansion ring 400 to contact the inner wall of the thin-walled cylinder for support. Multiple expansion rings 400 are distributed circumferentially along the second threaded sleeve 300; rotating the first threaded sleeve 200 allows for simultaneous adjustment of the positions of all expansion rings 400, making the adjustment process convenient.
[0029] The cooperation of the first threaded sleeve 200, the second threaded sleeve 300, and the expansion ring 400 allows for the synchronous adjustment of multiple expansion rings 400. At the same time, the radial position of the expansion ring 400 is adjusted by the rotational movement of the first threaded sleeve 200, resulting in high adjustment accuracy. After the first threaded sleeve 200 is adjusted to the preset position, its position remains stable after the external driving force is released, thus ensuring the stability of the position of the expansion ring 400.
[0030] The rotation of the first threaded sleeve 200 requires the cooperation of a fastening tool. The fastening tool is clamped into the annular cavity of the first threaded sleeve 200, and the first threaded sleeve 200 is driven to rotate by rotating the fastening tool. In some specific embodiments, the first threaded sleeve 200 can be an internal hexagonal threaded sleeve, and the fastening tool can be an external hexagonal wrench. The external hexagonal wrench is used to cooperate with the first threaded sleeve 200 to drive the first threaded sleeve 200 to rotate.
[0031] In some embodiments, a compression spring 500 is also connected between the expansion ring 400 and the mounting base 100. The axial direction of the compression spring 500 is the same as the direction of movement of the expansion ring 400 relative to the mounting base 100. When the expansion ring 400 moves radially away from the second threaded sleeve 300, the expansion ring 400 can compress the spring 500. The compressed spring can provide a driving force to the expansion ring 400, causing the expansion ring 400 to tend to move closer to the second threaded sleeve 300.
[0032] When adjusting the expansion ring 400 away from the second threaded sleeve 300, the position of the expansion ring 400 is adjusted by the support at the contact point between the second threaded sleeve 300 and the expansion ring 400. Since at least one of the first mating surface 310 and the second mating surface 420 is inclined, the expansion ring 400 is pushed away from the second threaded sleeve 300 as the second threaded sleeve 300 moves axially. When adjusting the expansion ring 400 towards the second threaded sleeve 300, the first threaded sleeve 200 is rotated in the opposite direction, and the second threaded sleeve 300 moves in the opposite direction. The compression spring 500 ensures that the expansion ring 400 remains pressed against the second threaded sleeve 300, and the second mating surface 420 and the first mating surface 310 remain in contact. As the second threaded sleeve 300 moves, the expansion ring 400 adjusts its position accordingly, thereby smoothly adjusting the expansion tire assembly to the preset size.
[0033] In some embodiments, the compression spring 500 can be directly fixed between the expansion ring 400 and the mounting base 100. In other embodiments, refer to... Figure 4 As shown, a mounting groove 430 is provided on the side wall of the expansion ring 400. The expansion tire assembly also includes an expansion ring retaining pin 600, one end of which is fixed to the mounting base 100, and the other end extends into the mounting groove 430. When adjusting the position of the expansion ring 400, the expansion ring retaining pin 600 moves within the mounting groove 430 without interfering with the movement of the expansion ring 400. A compression spring 500 is located within the mounting groove 430 and on the side of the expansion ring retaining pin 600 closest to the second threaded sleeve 300. The compression spring 500 is fixed between the side wall of the mounting groove 430 and the expansion ring retaining pin 600.
[0034] As the expansion ring 400 moves away from the mounting base 100 in a direction away from the second threaded sleeve 300, the expansion ring retaining pin 600 engages with the side wall of the mounting groove 430 to compress the compression spring 500. By fixing the compression spring 500 with the expansion ring retaining pin 600, the compression spring 500 is confined within the mounting groove 430, ensuring that the compression spring 500 can be compressed smoothly.
[0035] In some preferred embodiments, reference Figure 4As shown, both the first mating surface 310 and the second mating surface 420 are planar structures, and both are inclined relative to the axis of the second threaded sleeve 300. Along the axial direction of the second threaded sleeve 300, the distance between the first mating surface 310 and the second mating surface 420 and the axis of the second threaded sleeve 300 gradually decreases. The first mating surface 310 and the second mating surface 420 are in surface contact with each other, and the outer peripheral surface of the second threaded sleeve 300 is conical. The first mating surface 310 and the second mating surface 420 are both inclined in the same direction, and they are in surface contact with each other, that is, their inclination angles relative to the axis of the second threaded sleeve 300 are the same. The surface contact between the second mating surface 420 and the first mating surface 310 can improve the contact stability between the second threaded sleeve 300 and the expansion ring 400, so as to ensure the smoothness of the adjustment of the position of the expansion ring 400.
[0036] In some preferred embodiments, multiple expansion rings 400 are evenly distributed along the circumference of the second threaded sleeve 300, so that the arc-shaped support surface 410 at the end of the expansion ring 400 can uniformly support the thin-walled cylinder in the circumferential direction, avoiding uneven stress on the thin-walled cylinder. In some specific embodiments, the expansion tire assembly includes eight expansion rings 400, as can be referred to... Figure 1 and Figure 5 As shown, eight expansion rings 400 are evenly distributed along the circumference of the second threaded sleeve 300, and the eight expansion rings 400 correspond to eight first mating surfaces 310, which are evenly distributed on the outer peripheral wall of the second threaded sleeve 300.
[0037] The number of expansion rings 400 should not be too many, as too many expansion rings 400 will make the overall structure of the tire expansion assembly too complex; the number of expansion rings 400 should not be too few either, as too few expansion rings 400 will cause the stress on the thin-walled cylindrical parts to be more concentrated, and the thin-walled cylindrical parts will be at greater risk of deformation.
[0038] This application embodiment also provides an internal support fixture, including an internal support tube 700 and a plurality of expansion tire components provided in the above embodiments. The plurality of expansion tire components are distributed along the axial direction of the internal support tube 700. The mounting base 100 is installed on the internal support tube 700 and is coaxially arranged with the internal support tube 700. The inner diameter of the first threaded sleeve 200 is smaller than the inner diameter of the internal support tube 700.
[0039] Multiple expansion tire assemblies are connected to the inner support tube 700, which can provide stable support for thin-walled cylindrical components with a long axial length. The more expansion tire assemblies there are, the longer the thin-walled cylindrical component can be supported.
[0040] The inner diameter of the first threaded sleeve 200 is smaller than that of the inner support tube 700. A fastening tool for driving the first threaded sleeve 200 can extend from the end of the inner support tube 700 into the inner support tube 700 and engage with the first threaded sleeve 200, thus driving its rotation. The inner diameter of the inner support tube 700 is larger, allowing the fastening tool to freely extend into it without interfering with its rotation, facilitating the use of the inner support fixture.
[0041] The mounting base 100 has an annular structure and is directly fixed to the inner support tube 700. Since the inner diameter of the first threaded sleeve 200 is smaller than that of the inner support tube 700, a portion of the first threaded sleeve 200 is actually located inside the inner support tube 700. Therefore, the inner support tube 700 is actually provided with an annular groove. The mounting base 100 is fixed to the area of the annular groove, allowing a portion of the first threaded sleeve 200 to be located inside the inner support tube 700. In effect, this divides the inner support tube 700 into several segments, with adjacent tire expansion assemblies fixed together through one segment of the inner support tube 700.
[0042] For the fitting of the internal support fixture and the 900 part to be supported, please refer to [reference needed]. Figure 6 As shown, the expansion ring 400 abuts against the inner wall of the part to be supported 900, thus supporting the part to be supported 900. The part to be supported 900 is the thin-walled cylindrical part that needs to be processed.
[0043] In some preferred embodiments, four sets of expansion tire assemblies are provided, which are sequentially distributed along the axial direction of the inner support tube 700. The inner diameter of the first threaded sleeve 200 of the two middle sets of expansion tire assemblies is smaller than that of the first threaded sleeve 200 of the two outer sets. Because the inner diameter of the middle first threaded sleeve 200 is smaller, the corresponding fastening tool can pass through the two outer first threaded sleeves 200 and extend into the middle first threaded sleeve 200. More preferably, the inner diameter of the outer threaded sleeves can be set to be larger, so that the fastening tool corresponding to the middle first threaded sleeve 200 can rotate freely within the two outer first threaded sleeves 200, facilitating the rotation of the middle first threaded sleeve 200.
[0044] In some embodiments, end caps 800 are fixedly connected to both ends of the inner support tube 700, for reference. Figure 6 As shown, the end cap 800 is fitted over the inner support tube 700. The presence of the end cap 800 facilitates the clamping of the entire inner support fixture. The connection between the end cap 800 and the inner support tube 700 can be configured as a detachable connection, so that the end cap 800 can be replaced even if it is damaged during clamping.
[0045] The inner wall of the inner support tube 700 is provided with a guide surface, which is located at the end of the inner support tube 700. Along the axial direction of the support tube, the radial dimension of the guide surface gradually decreases from the outside towards the inner support tube 700. The closer to the outside, the larger the radial dimension of the guide surface. The guide surface can guide the fastening tool inserted into the inner support tube 700, facilitating the smooth insertion of the fastening tool into the inner support tube 700. When end caps 800 are fixed at both ends of the inner support tube 700, the guide surface can also be provided at the inner peripheral wall of the end caps 800.
[0046] The internal support fixture provided in this embodiment only requires rotating the first internal threaded sleeve 200 to support the inner wall of the thin-walled cylindrical component. Furthermore, the expansion ring 400 can be adjusted to move towards the second threaded sleeve 300, reducing the overall radial dimension of the expansion assembly, making disassembly easier after use. When the workpiece is long, a corresponding number of expansion assemblies can be added. Moreover, the inner diameter of the first threaded sleeve 200 increases sequentially from the expansion assembly located in the middle towards both sides, facilitating adjustment of the radial dimension of the expansion assembly.
[0047] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0048] The above description is only a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model.
Claims
1. A tire expansion assembly, characterized in that, Includes mounting base, first threaded sleeve, second threaded sleeve, and multiple expansion rings; The mounting base is an annular structure and is coaxially arranged with the first threaded sleeve and the second threaded sleeve. The first threaded sleeve is rotatably mounted on the mounting base and is axially limited to the mounting base. The second threaded sleeve is threaded onto the outside of the first threaded sleeve. The outer peripheral wall of the second threaded sleeve includes a plurality of first mating surfaces distributed along its circumference. The expansion ring is movably connected to the mounting base along the radial direction of the second threaded sleeve. One end of the expansion ring is provided with an arc-shaped support surface, and the other end is provided with a second mating surface that contacts the first mating surface. The expansion ring corresponds one-to-one with the first mating surface, and at least one of the first mating surface and the second mating surface is inclined relative to the axis of the second threaded sleeve. The first threaded sleeve can rotate under the action of an external force to drive the second threaded sleeve to move along its axial direction, thereby pushing the expansion ring to move radially along the second threaded sleeve.
2. The tire expansion assembly according to claim 1, characterized in that, A compression spring is also connected between the expansion ring and the mounting base. The axial direction of the compression spring is the same as the direction of movement of the expansion ring relative to the mounting base. When the expansion ring moves radially away from the second threaded sleeve, the expansion ring can compress the compression spring.
3. The tire expansion assembly according to claim 2, characterized in that, The expansion ring sidewall is provided with an installation groove, and the expansion tire assembly also includes an expansion ring retaining pin. One end of the expansion ring retaining pin is fixed to the mounting base, and the other end extends into the installation groove. The compression spring is located in the installation groove and is located on the side of the expansion ring retaining pin near the second threaded sleeve. The compression spring is fixed between the sidewall of the installation groove and the expansion ring retaining pin. When the expansion ring moves away from the mounting base in a direction away from the second threaded sleeve, the expansion ring retaining pin engages with the side wall of the mounting groove to compress the compression spring.
4. The tire expansion assembly according to claim 1, characterized in that, Both the first mating surface and the second mating surface are planar structures and are inclined relative to the axis of the second threaded sleeve. Along the axial direction of the second threaded sleeve, the distance between the first mating surface and the second mating surface and the axis of the second threaded sleeve gradually decreases, and the first mating surface and the second mating surface are in surface contact with each other.
5. The tire expansion assembly according to claim 1, characterized in that, The plurality of expansion rings are evenly distributed along the circumference of the second threaded sleeve.
6. A tire expansion assembly according to claim 5, characterized in that, The tire expansion assembly includes eight expansion rings, which are evenly distributed circumferentially along the second threaded sleeve.
7. An internal support fixture, characterized in that, The device includes an inner support tube and a plurality of tire expansion components as described in any one of claims 1-6, wherein the plurality of tire expansion components are distributed along the axial direction of the inner support tube, the mounting base is mounted on the inner support tube and coaxially arranged with the inner support tube, and the inner diameter of the first threaded sleeve is smaller than the inner diameter of the inner support tube.
8. The internal support fixture according to claim 7, characterized in that, The tire expansion assembly has four sets, and the inner diameter of the first threaded sleeve of the middle two sets of tire expansion assemblies is smaller than that of the first threaded sleeve of the tire expansion assemblies on both sides.
9. The internal support fixture according to claim 7, characterized in that, Both ends of the inner support tube are fixedly connected to end caps, which are sleeved on the outside of the inner support tube.
10. The internal support fixture according to claim 7, characterized in that, The inner wall of the inner support tube is provided with a guide surface, which is located at the end of the inner support tube and extends from the outside toward the inner support tube along the axial direction of the support tube. The radial dimension of the guide surface gradually decreases.