Concrete form for hole formation

Abstract

To improve the workability of work to insert reinforcing bars etc. with respect to a concrete form for hole formation capable of forming an axial hole having unevenness in a concrete molding.SOLUTION: A concrete form 1 for hole formation used for forming a hole 3 with axial unevenness at least in part in a peripheral direction in a concrete molding (2A, 2B) has: an expansion pipe 8 which can expand radially outward as fluid is introduced; a plurality of rigid members 9 which is arranged peripherally around the expansion pipe; and an expandable elastic pipe 10 which includes the expansion pipe and the plurality of rigid members inside, and can expand radially outward as the expansion pipe expands. The expansion pipe, the rigid members and the elastic pipe all extend in an axial direction. The elastic pipe has an outer peripheral surface forming an inner peripheral surface of the hole. The outer peripheral surface of the elastic pipe has a plurality of projections 28 which protrudes outward from the outer peripheral surface to form an uneven part of unevenness, and a first smooth surface 25 formed smoothly in the axial direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a formwork for forming holes in a concrete molded body.

Background Art

[0002] Conventionally, holes for inserting reinforcing bars or the like may be provided in a concrete molded body formed by placing concrete in a formwork. After inserting a reinforcing bar or the like into the hole, a filling material such as non-shrink grout is injected. Due to the solidification of the filling material, the reinforcing bar or the like inserted into the hole is fixed to the concrete molded body via the filling material. In order to improve the fixing force of the reinforcing bar or the like inserted into the hole with respect to the concrete molded body, unevenness may be provided on the inner peripheral surface of the hole.

[0003] Patent Document 1 discloses a formwork for forming holes in a concrete molded body. The hole forming member has a core pipe (core body) and a belt wound around the core pipe. Protrusions (ridges) are provided on the outer surface of the belt. Thereby, when the belt is wound around the core pipe, the outer peripheral surface of the hole forming formwork has an uneven shape. After the hole forming formwork is arranged in the formwork of the concrete molded body, fluid concrete is placed in the formwork. By the solidification of the placed concrete, a hole having an inner surface with an uneven shape corresponding to the uneven shape of the hole forming formwork is formed. After the concrete is solidified and the core pipe is removed from the concrete molded body, the hole forming formwork is pulled out from the hole formed in the concrete molded body by pulling the end of the belt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a reinforcing bar or the like is inserted into a hole formed by the hole-forming formwork of Patent Document 1, there is a risk that the tip of the reinforcing bar or the like will be caught by the uneven portions of the hole. This may reduce the workability of the operation of inserting the reinforcing bar or the like.

[0006] In view of the above background, an object of the present invention is to improve the workability of the operation of inserting a reinforcing bar or the like in a hole-forming formwork capable of forming a hole having unevenness along the axial direction in a concrete molded body.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention provides a hole-forming formwork (1) for forming a hole (3) having unevenness along the axial direction in at least a part of the circumferential direction in a concrete molded body (2A, 2B), the hole-forming formwork (1) including an expansion tube (8) that extends along the axial direction and is expandable radially outward by introducing a fluid, a plurality of rigid members (9) that extend along the axial direction and are arranged along the circumferential direction of the expansion tube, and an elastic tube (10) that extends along the axial direction, encloses the expansion tube and the plurality of rigid members, and is expandable radially outward in response to the expansion of the expansion tube. The elastic tube has an outer peripheral surface that forms the inner peripheral surface of the hole, and the outer peripheral surface of the elastic tube has a plurality of convex portions (28) that protrude outward from the outer peripheral surface to form concave portions of the unevenness, and a first smooth surface (25) that is smoothly formed along the axial direction.

[0008] According to this aspect, the inner peripheral surface of the hole formed in the concrete molded body by the hole-forming formwork is smooth along the axial direction of the hole in the portion corresponding to the first smooth surface. Therefore, when a reinforcing bar or the like is inserted along the portion of the inner peripheral surface of the hole corresponding to the first smooth surface, the catching of the reinforcing bar or the like on the inner peripheral surface of the hole is suppressed. Accordingly, the workability of the operation of inserting the reinforcing bar or the like is improved.

[0009] In the above aspect, the axial direction is the horizontal direction, and in the formation of the hole, the hole-forming formwork may be arranged such that the first smooth surface faces downward.

[0010] When a reinforcing bar or the like is inserted into a hole extending in the horizontal direction, typically, the reinforcing bar or the like is inserted into the hole in a state where the tip of the reinforcing bar or the like is deflected downward due to its own weight. According to this aspect, the inner peripheral surface of the hole formed in the concrete molded body becomes smooth along the axial direction at the lower end. Therefore, by inserting the deflected tip of the reinforcing bar or the like along the lower end of the inner peripheral surface of the hole corresponding to the first smooth surface, the snagging of the reinforcing bar or the like on the inner peripheral surface of the hole is suppressed.

[0011] In the above aspect, it is preferable that the outer peripheral surface of the elastic tube has a second smooth surface (26) facing the first smooth surface and smoothly formed along the axial direction.

[0012] According to this aspect, the inner peripheral surface of the hole formed in the concrete molded body becomes smooth along the axial direction at the upper end. Therefore, when the hole is filled with a filler, the retention of air bubbles in the hole is suppressed.

[0013] In the above aspect, it is preferable that the plurality of convex portions form ridges extending in the circumferential direction, and at the end of the ridge close to the second smooth surface, the radial dimension of the ridge is smaller as it is closer to the second smooth surface.

[0014] According to this aspect, a concave groove is formed in the inner peripheral surface of the hole formed in the concrete molded body at a portion corresponding to the ridge of the elastic tube, and the concave groove gradually becomes shallower toward the smooth upper end at the end. Therefore, when the hole is filled with a filler, the retention of air bubbles at the upper end of the concave groove is more effectively suppressed.

[0015] In the above aspect, it is preferable that at the end of the ridge close to the first smooth surface, the radial dimension of the ridge is smaller as it is closer to the first smooth surface.

[0016] According to this aspect, even when the hole-forming formwork is arranged so that the first smooth surface faces upward, the concave groove formed in the inner peripheral surface of the hole formed in the concrete molded body gradually becomes shallower toward the smooth upper end, and the retention of air bubbles in the concave groove is suppressed. Therefore, the operator can arrange the hole-forming formwork without worrying about the up-and-down direction.

[0017] In the above aspect, it is preferable that the outer peripheral surface of at least one end portion of the elastic tube has an annular smooth surface (24) formed smoothly along the axial direction and the circumferential direction.

[0018] According to this aspect, when the hole-forming formwork is inserted and arranged in, for example, a mechanical joint, the annular smooth surface comes into close contact with the inner peripheral surface of the mechanical joint due to the expansion of the elastic tube. Thereby, when placing concrete, the inflow of concrete into the inside of the mechanical joint is suppressed.

Advantages of the Invention

[0019] The present invention can improve the workability of the operation of inserting a reinforcing bar or the like in a hole-forming formwork capable of forming a hole having unevenness along the axial direction in a concrete molded body.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Best Mode for Carrying Out the Invention

[0021] Hereinafter, with reference to the drawings, an embodiment of the hole-forming formwork 1 according to the present invention will be described. The hole-forming formwork 1 (see FIG. 2) is a formwork for forming holes 3 in a concrete molded body. Specifically, as shown in FIG. 1, holes 3 are formed in a column member 2A and a first beam member 2B made of precast concrete.

[0022] The hole 3 formed in the column member 2A is a horizontal through-hole that penetrates the column member 2A in the horizontal direction. The hole 3 formed in the first beam member 2B is a communication hole that extends horizontally from the joint surface of the first beam member 2B that joins the column member 2A to a mechanical joint 5 embedded inside the first beam member 2B. In the holes 3 of these column member 2A and first beam member 2B, a beam main reinforcement 4 protruding from the end face of a second beam member 2C arranged on the side of the first beam member 2B opposite to the column member 2A is inserted. The beam main reinforcement 4 is received inside the corresponding hole 3 and mechanical joint 5, and in this state, a filler 6 (see FIG. 8) such as non-shrink grout is injected from an injection / discharge hole 7 provided in the mechanical joint 5, whereby the holes 3 and the inside of the mechanical joint 5 are filled with the filler 6. When the filler 6 hardens, the beam main reinforcement 4 is fixed to the first beam member 2B and the column member 2A via the filler 6.

[0023] Hereinafter, the axial direction of the hole 3 will be defined as the front-rear direction, and the left-right and up-down directions will be defined for description.

[0024] As shown in FIG. 2, the hole-forming formwork 1 has an expansion tube 8 that can expand radially outward by introducing a fluid, a plurality of rigid members 9 arranged along the circumferential direction of the expansion tube 8, and an elastic tube 10 that encloses the expansion tube 8 and the plurality of rigid members 9 and can expand radially outward in response to the expansion of the expansion tube 8. The expansion tube 8, the plurality of rigid members 9, and the elastic tube 10 all extend in the front-rear direction.

[0025] The expansion tube 8 may be a known cylindrical member having, for example, two rubber layers and a plurality of reinforcing threads disposed between the two rubber layers and aligned in the front-rear direction. For a more detailed configuration, refer to the rubber expansion tube described in Japanese Patent No. 5396026. When fluid is introduced into the interior of the expansion tube 8, the expansion tube 8 expands so that its diameter increases. When the expansion tube 8 expands, the contraction of the expansion tube 8 in the front-rear direction is suppressed by the reinforcing threads.

[0026] As shown in conjunction with FIG. 3, at the front end of the expansion tube 8, a coupler 12 and a base metal fitting 13 for injecting fluid into the interior of the expansion tube 8 or discharging the fluid inside the expansion tube 8 are provided. The portion from the central portion to the rear end of the base metal fitting 13 is inserted into the expansion tube 8. The coupler 12 is connected to the front end of the base metal fitting 13. At the rear end of the expansion tube 8, an end cap 14 is provided. The portion from the central portion to the front end of the end cap 14 is inserted into the expansion tube 8. On the outer peripheral surface of the end of the expansion tube 8 into which the base metal fitting 13 and the end cap 14 are inserted, a sleeve 15 smaller in diameter than the expansion tube 8 is provided. The sleeve 15 suppresses the base metal fitting 13 and the end cap 14 from coming out of the expansion tube 8.

[0027] The rigid member 9 is formed of a steel piece that is arcuate in a front cross-sectional view seen from the front. The rigid member 9 may be formed, for example, by dividing a cylindrical steel pipe. In the present embodiment, three rigid members 9 are arranged along the outer peripheral surface of the expansion tube 8.

[0028] The hole-forming formwork 1 extends in the front-rear direction and has a holding portion 16 for holding each rigid member 9. The holding portion 16 is formed of a cloth that is difficult to stretch, such as hemp or cotton, for example. The holding portion 16 has a cylindrical main body sheet 17 that encloses the expansion tube 8 and a plurality of holding sheets 18 disposed on the outer peripheral surface of the main body sheet 17. The diameter of the main body sheet 17 is set to a predetermined diameter corresponding to the diameter of the hole 3 formed in the concrete molded body.

[0029] Each of the plurality of holding sheets 18 may be formed in a cylindrical shape larger than the diameter of the main body sheet 17. The length of the holding sheet 18 in the front-rear direction is set to be smaller than the length of the main body sheet 17 in the front-rear direction. In the present embodiment, three holding sheets 18 are arranged at intervals in the front-rear direction. Each holding sheet 18 is arranged at the front end portion, the central portion, and the rear end portion of the main body sheet 17.

[0030] As shown in FIGS. 2, 3, 5, and 6, the holding portion 16 has a plurality of connecting portions 20 in which a part of the holding sheet 18 and a part of the main body sheet 17 are connected to each other. In the present embodiment, three connecting portions 20 are provided for one holding sheet 18. The three connecting portions 20 are provided at substantially equal intervals in the circumferential direction of the main body sheet 17. Each connecting portion 20 has a predetermined dimension along the circumferential direction of the main body sheet 17.

[0031] Between the holding sheet 18 and the main body sheet 17, three spaces 21 defined by the inner circumferential surface of the holding sheet 18, the outer circumferential surface of the main body sheet 17, and two adjacent connecting portions 20 are formed. The front-rear direction of the space 21 is open. The spaces 21 formed between each holding sheet 18 and the main body sheet 17 are aligned in the front-rear direction view. Specifically, the space 21 formed by the holding sheet 18 provided at the front end portion of the main body sheet 17 and the corresponding space 21 formed by the holding sheet 18 provided at the central portion of the main body sheet 17 are aligned in the front-rear direction view. Also, the space 21 formed by the holding sheet 18 provided at the central portion of the main body sheet 17 and the corresponding space 21 formed by the holding sheet 18 provided at the rear end portion of the main body sheet 17 are aligned in the front-rear direction view. The rigid member 9 passes through the corresponding space 21 and is held by the holding portion 16.

[0032] In another embodiment, the rear of the space 21 formed by the holding sheet 18 provided at the rear end portion of the main body sheet 17 may be closed. Thereby, the rearward escape of the rigid member 9 is suppressed.

[0033] As shown in FIGS. 2 and 4, the elastic tube 10 is made of rubber and has a cylindrical shape. The outer peripheral surface of the rear end portion of the elastic tube 10 has an annular smooth surface 24 that is smoothly formed along the front-rear direction and the circumferential direction. Further, the outer peripheral surface of the elastic tube 10 has a first smooth surface 25 (see FIG. 5) and a second smooth surface 26 that are smoothly formed along the front-rear direction. The first smooth surface 25 and the second smooth surface 26 are provided from the front end of the elastic tube 10 to the front end of the annular smooth surface 24. The first smooth surface 25 and the second smooth surface 26 are provided at positions facing each other.

[0034] The outer peripheral surface of the elastic tube 10 further has a plurality of ridges 28 as a plurality of convex portions that protrude radially outward from the outer peripheral surface of the elastic tube 10. The ridges 28 are integrally formed with the elastic tube 10. The ridges 28 extend along the circumferential direction of the outer peripheral surface from the first smooth surface 25 to the second smooth surface 26. The ridges 28 are provided on both the left and right sides of the first smooth surface 25 and the second smooth surface 26. The ridges 28 provided on the outer peripheral surface on one side and the ridges 28 provided on the outer peripheral surface on the other side are provided facing each other.

[0035] At each end portion of the ridge 28 close to the first smooth surface 25 and the second smooth surface 26, the radial dimension of the ridge 28 is smaller as it is closer to the first smooth surface 25 and the second smooth surface 26. Specifically, the width dimension from the end portion of the ridge 28 on the side of the first smooth surface 25 to the end portion of the ridge 28 on the side of the second smooth surface 26 is set to be substantially equal to the outer diameter of the elastic tube 10. The elastic tube 10 has a shape that is line-symmetric with respect to a line in the left-right direction passing through the center of the elastic tube 10 in a front cross-sectional view.

[0036] In other embodiments, the width dimension from the end portion of the ridge 28 on the side of the first smooth surface 25 to the end portion of the ridge 28 on the side of the second smooth surface 26 may be set to be smaller as it is farther from the first smooth surface 25 and the second smooth surface 26.

[0037] As shown in FIGS. 5(A) and 6(A), in a state where no fluid is introduced into the expansion tube 8, the connection portion 20 of the holding portion 16 is loose. That is, each rigid member 9 is enclosed in the elastic tube 10 in a state of being close to each other.

[0038] When fluid is introduced into the expansion tube 8, each rigid member 9 moves radially outward so as to be separated from each other in response to the expansion of the expansion tube 8. Due to the movement of each rigid member 9, the elastic tube 10 expands radially outward so that its diameter increases. As shown in FIGS. 5(B) and 6(B), when fluid is introduced into the expansion tube 8, the connecting portion 20 of the holding portion 16 is in a fully extended state. Since the holding portion 16 is formed of a cloth that is difficult to stretch, even if fluid is excessively introduced into the expansion tube 8, a predetermined diameter can be maintained. Thereby, excessive expansion of the elastic tube 10 is suppressed.

[0039] The operation of forming the hole 3 in the concrete molded body will be described. Hereinafter, the hole 3 of the first beam member 2B shown in FIG. 1 will be described as an example.

[0040] First, the operator arranges the hole-forming form 1 at a predetermined position within the form for forming the first beam member 2B. Reinforcing bars such as main reinforcing bars (not shown) are assembled in the form in advance. At this time, no fluid is introduced into the expansion tube 8. Further, the operator arranges the hole-forming form 1 so that the first smooth surface 25 faces downward. Thereby, the second smooth surface 26 faces upward, and the outer peripheral surface including the protrusion 28 faces in the left-right direction. Since the elastic tube 10 has a line-symmetric shape, the operator may arrange the hole-forming form 1 without worrying about the up-down direction, that is, so that the second smooth surface 26 faces downward. Further, the operator inserts the rear end portion of the elastic tube 10 provided with the annular smooth surface 24 into the mechanical joint 5. Next, the operator introduces fluid into the expansion tube 8 to expand the elastic tube 10.

[0041] Thereafter, the operator places the fluidized concrete into the form. Since the annular smooth surface 24 is in close contact with the inner peripheral surface of the mechanical joint 5 due to the expansion of the elastic tube 10, the inflow of the fluidized concrete into the inside of the mechanical joint 5 is suppressed.

[0042] By placing concrete, a first beam member 2B having a hole 3 with an inner peripheral surface corresponding to the outer peripheral surface shape of the elastic tube 10 is formed. Specifically, due to the protrusions 28 provided on the outer peripheral surface of the elastic tube 10, concave ridges are formed on the portions of the inner peripheral surface of the corresponding hole 3, and due to the concave ridge portions between the adjacent protrusions 28, protrusions are formed on the portions of the inner peripheral surface of the corresponding hole 3. As a result, on the inner peripheral surface of the hole 3, unevenness along the front-rear direction is formed on both the left and right side surfaces. Also, due to the first smooth surface 25 and the second smooth surface 26 provided on the outer peripheral surface of the elastic tube 10, the upper end surface and the lower end surface of the inner peripheral surface of the corresponding hole 3 are formed smoothly along the front-rear direction. Since the radial dimension at the end of the protrusion 28 formed on the elastic tube 10 is smaller the closer it is to the first smooth surface 25 and the second smooth surface 26, the concave ridges formed on the inner peripheral surface of the hole 3 gradually become shallower towards the smooth upper end surface and lower end surface of the inner peripheral surface of the hole 3 at the ends.

[0043] After the placed concrete solidifies, fluid is discharged from the expansion tube 8 to release the expansion of the elastic tube 10. Then the operator extracts the hole-forming formwork 1 from the first beam member 2B. Thereby, a hole 3 is formed in the first beam member 2B. By releasing the expansion of the elastic tube 10, since the outer diameter of the elastic tube 10 after the expansion is released becomes smaller than the diameter of the hole 3, the operator can easily extract the hole-forming formwork 1 from the first beam member 2B.

[0044] Next, with reference to FIGS. 7 and 8, the effects of the hole 3 formed by the hole-forming formwork 1 of the present invention will be described in comparison with the prior art. Here, the hole 3 of the first beam member 2B shown in FIG. 1 will also be used as an example for explanation.

[0045] FIGS. 7(A) and 8(A) show the hole 3 formed by the prior art hole-forming formwork. That is, unevenness along the front-rear direction is formed on the upper end surface and the lower end surface of the inner peripheral surface of the hole 3. FIGS. 7(B) and 8(B) show the hole 3 formed by the hole-forming formwork 1 of the present invention. That is, the upper end surface and the lower end surface of the inner peripheral surface of the hole 3 are formed smoothly along the front-rear direction.

[0046] As shown in Fig. 7, a beam main reinforcement 4 protruding from the end face of the second beam member 2C is inserted into the hole 3. At this time, since the beam main reinforcement 4 is arranged to extend in the front-rear direction, the front end portion of the beam main reinforcement 4 deflects downward due to its own weight. Therefore, when the beam main reinforcement 4 is inserted into the hole 3, the front end portion of the beam main reinforcement 4 is likely to contact the lower end face of the inner peripheral surface of the hole 3. As shown in Fig. 7(A), since the front end portion of the beam main reinforcement 4 is caught by the unevenness formed on the lower end face of the inner peripheral surface of the hole 3, the workability of the operation of inserting the beam main reinforcement 4 is reduced. On the other hand, as shown in Fig. 7(B), the operator inserts the beam main reinforcement 4 along the smooth lower end face of the inner peripheral surface of the hole 3, thereby suppressing the catching of the beam main reinforcement 4 with respect to the inner peripheral surface of the hole 3. Therefore, the workability of the operation of inserting the beam main reinforcement 4 is improved.

[0047] As shown in Fig. 8, a filler 6 such as non-shrinkage grout is injected into the hole 3 into which the beam main reinforcement 4 is inserted. The filler 6 is filled while pushing out the air existing in the hole 3. As shown in Fig. 8(A), the extrusion of air by the filler 6 is hindered by the unevenness provided on the upper end face of the inner peripheral surface of the hole 3. As a result, air bubbles 30 remain between the concave strip provided on the upper end face of the inner peripheral surface of the hole 3 and the filler 6. On the other hand, as shown in Fig. 8(B), since the upper end face of the inner peripheral surface of the hole 3 is smoothly formed along the front-rear direction, the extrusion of air by the filler 6 is not hindered. Therefore, the retention of the air bubbles 30 in the hole 3 is suppressed. The concave strip formed on the inner peripheral surface of the hole 3 gradually becomes shallower toward the smooth upper end face of the inner peripheral surface of the hole 3 at the upper end portion. Thereby, the air existing at the upper end portion of the concave strip formed on the inner peripheral surface of the hole 3 is pushed out by the filler 6 to the smooth upper end face of the inner peripheral surface of the hole 3 corresponding to the second smooth surface 26. Therefore, the retention of the air bubbles 30 is more effectively suppressed.

[0048] With the above description of the specific embodiments completed, the present invention is not limited to the above embodiments and variations, and can be widely modified and implemented. For example, in the above embodiment, the protrusion 28 is provided on the outer peripheral surface of the elastic tube 10, but a plurality of convex portions may be provided. In this case, a concave portion is formed on the inner peripheral surface of the hole 3 at a portion corresponding to the convex portion of the elastic tube 10. Further, although the annular smooth surface 24 is formed at one end of the elastic tube 10, it may be formed at both ends of the elastic tube 10. Furthermore, a plurality of elastic tubes 10 having different shapes from each other may be prepared, and the elastic tube 10 may be appropriately selected according to the use of the hole 3. The specific configurations, arrangements, quantities, materials, etc. of each member and part can be appropriately changed as long as they do not deviate from the gist of the present invention. Also, not all of the constituent elements shown in the above embodiments are necessarily essential, and can be appropriately selected.

Explanation of Reference Numerals

[0049] 1: Formwork for hole formation 2A: Column member (concrete molded body) 2B: First beam member (concrete molded body) 3: Hole 8: Expansion tube 9: Rigid member 10: Elastic tube 24: Annular smooth surface 25: First smooth surface 26: Second smooth surface 28: Protrusion (convex portion)

Claims

1. A hole forming form for forming a hole having an axially-oriented unevenness in at least a portion of a circumferential direction in a concrete molded body, an expansion tube extending along the axial direction and capable of expanding radially outward by the introduction of a fluid; a plurality of rigid members extending along the axial direction and arranged along a circumferential direction of the expansion tube; an elastic tube extending along the axial direction, containing the expansion tube and the plurality of rigid members, and capable of expanding radially outward in response to expansion of the expansion tube; the elastic tube has an outer circumferential surface that forms an inner circumferential surface of the hole, The outer peripheral surface of the elastic tube has a plurality of convex portions protruding outward from the outer peripheral surface to form concave portions of the unevenness, and a first smooth surface formed smoothly along the axial direction.

2. The axial direction is a horizontal direction, The hole forming form according to claim 1 , wherein, in forming the hole, the hole forming form is arranged so that the first smooth surface faces downward.

3. 3. The hole forming form according to claim 2, wherein the outer peripheral surface of the elastic tube has a second smooth surface that faces the first smooth surface and is smoothly formed along the axial direction.

4. The hole forming form according to claim 3, wherein the plurality of convex portions form ridges extending in the circumferential direction, and at the end of the ridge closer to the second smooth surface, the radial dimension of the ridge is smaller the closer to the second smooth surface.

5. 5. The hole forming form according to claim 4, wherein a radial dimension of the ridge at an end portion of the ridge closer to the first smooth surface becomes smaller as the ridge approaches the first smooth surface.

6. 6. The hole forming form according to claim 1, wherein the outer peripheral surface of at least one end of the elastic tube has an annular smooth surface that is smoothly formed along the axial direction and the circumferential direction.

Images