Spring tube and its assembling method and assembling tool

Abstract

The application provides a spring tube, which comprises an inner layer tube, a spring and an outer layer tube arranged from inside to outside in sequence, the inner layer tube comprises a middle section and a hardened section arranged at least one end of the middle section and connected with the middle section, the end of the hardened section connected with the middle section is sleeved outside the middle section and connected with the middle section partially in overlap, and the inner wall of the hardened section is formed with a step; the spring is sleeved outside the inner layer tube and covers at least the middle section, the outer layer tube is sleeved outside the spring and covers the middle section and the hardened section, and the outer layer tube is connected with the hardened section in overlap. The application reduces the risk of blood injury and hemolysis.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, and more specifically, to a spring tube, its assembly method, and assembly tooling. Background Technology

[0002] In catheter pumps, the spring tube, as an integral part of the pump, helps the catheter maintain a certain degree of rigidity and flexibility as it advances through the blood vessel, preventing bending or collapse. Furthermore, the spring tube helps to fix the pump's position and maintain the stability of the blood flow path during operation.

[0003] The existing Bourdon tube technology has the following drawbacks: 1. When the two ends of the spring tube are connected to the rigid metal parts, the tube is covered by the rigid metal parts and a step is formed inside the connection between the spring tube and the rigid metal parts. Blood flows at high speed on the inner surface of the flow channel and hits the step, which damages the blood and may even cause hemolysis. 2. To prevent bending when passing through the sealing ring of the sheath tube, the spring tube is relatively rigid, which affects the geometric integrity of the pumping channel in high-pressure blood flow areas such as the aortic arch; 3. The rigidity requirement of the catheter is contradictory to miniaturization. In order to maintain power transmission efficiency, the spring tube needs to have a certain thickness, resulting in a large overall diameter of the catheter and making it difficult to bend.

[0004] Therefore, based on the problems existing in the prior art, it is necessary to provide a spring tube and its assembly method and assembly tooling. Summary of the Invention

[0005] In view of this, the present invention provides a spring tube, comprising an inner tube, a spring, and an outer tube arranged sequentially from the inside to the outside. The inner tube includes a middle section and a hardened section disposed at at least one end of the middle section and connected to the middle section. The end of the hardened section connected to the middle section is sleeved outside the middle section and partially overlaps with the middle section. The inner wall of the hardened section has a step. The spring is sleeved outside the inner tube and at least covers the middle section. The outer tube is sleeved outside the spring and covers the middle section and the hardened section. The outer tube overlaps with the hardened section.

[0006] Preferably, the length of the hardened section is 4mm-5mm, the length of the middle section is 60mm-62mm, and the overlap length between the hardened section and the middle section is 1mm-2mm.

[0007] Preferably, the hardness range of the hardened segment is 60D-75D, the hardness range of the intermediate segment is 80A-92A, and both the hardened segment and the intermediate segment are made of TPU.

[0008] Preferably, a developing ring is sleeved at the middle position outside the middle section, and the developing ring is located between the middle section and the spring.

[0009] Based on the same inventive concept, this application also provides a method for assembling the above-mentioned spring tube, wherein the spring tube includes an inner tube, a spring, and an outer tube arranged sequentially from the inside to the outside, the inner tube includes a middle section and a hardened section disposed at at least one end of the middle section and connected to the middle section, and the assembly method includes the following steps: a. Provide assembly tooling, the assembly tooling including an assembly liner and a step bushing; b. Provide an intermediate section and fit the intermediate section onto the assembled liner core; c. Provide a hardening segment, which is fitted over the outside of the proximal end of the assembled liner, and a portion of the hardening segment is fitted over the outside of the proximal end of the intermediate segment and overlaps with the proximal end of the intermediate segment. d. The stepped bushing is fitted onto the outside of the proximal end of the assembled liner, and the end of the stepped bushing with the smaller outer diameter is inserted between the hardened section and the assembled liner. e. Weld the hardened section to the middle section at the overlap; f. Provide a spring and sleeve the spring outside the middle section; g. Provide an outer tube, cover the inner tube on which the spring is sleeved, and weld the outer tube to the inner tube; h. Remove the stepped bushing and remove the assembled liner from the inner tube to complete the spring tube assembly.

[0010] Preferably, the assembled liner includes at least a first mounting section, a second mounting section, and a third mounting section coaxially connected in sequence, with the outer diameters of the first mounting section, the second mounting section, and the third mounting section increasing sequentially; the length of the second mounting section is equal to or slightly greater than the length of the intermediate section, and in step b, the intermediate section is fitted onto the second mounting section of the assembled liner.

[0011] Preferably, the length of the third mounting section is less than the length of the hardening section, and the hardening section consists of two sections respectively disposed at both ends of the intermediate section and connected to the intermediate section. Step b further includes providing the hardening section, fitting the hardening section onto the third mounting section of the assembled liner and partially located in the second mounting section, fitting the intermediate section onto the second mounting section of the assembled liner, such that the distal end of the intermediate section is disposed inside the hardening section and partially overlaps with the hardening section.

[0012] Preferably, the outer diameter of the smaller end of the stepped bushing is greater than the outer diameter of the second mounting section, the inner diameter of the stepped bushing matches the outer diameter of the first mounting section, and the length of the smaller end of the stepped bushing is less than the length of the hardening section. In step d, the stepped bushing is fitted onto the outside of the first mounting section of the assembled liner, and the smaller end of the stepped bushing is inserted between the hardening section and the assembled liner.

[0013] Preferably, step e includes: providing a first heat shrink tubing, wrapping the hardened section and the intermediate section with the first heat shrink tubing, performing heat shrinking, and removing the first heat shrink tubing after the hardened section and the intermediate section are fused together at the overlap.

[0014] Preferably, before step f, the method further includes: providing a developing ring and fitting the developing ring into the middle position outside the intermediate segment.

[0015] Preferably, step g includes: providing a second heat shrink tube, sleeve the second heat shrink tube over the outer tube, heat shrinking it, and removing the second heat shrink tube after the inner tube and the outer tube are fused together at the overlap.

[0016] Preferably, after step h, the assembly of the spring tube is further included in the following steps: bending and shaping the assembled spring tube.

[0017] Based on the same inventive concept, this application also provides an assembly fixture for the above-mentioned assembly method of the spring tube. The assembly fixture includes an assembly core and a stepped bushing. The assembly core includes a first mounting section, a second mounting section, and a third mounting section coaxially connected in sequence. The outer diameters of the first mounting section, the second mounting section, and the third mounting section increase sequentially. The length of the second mounting section is equal to or slightly greater than the length of the intermediate section, and the length of the third mounting section is less than the length of the hardened section. The outer diameter of the smaller end of the stepped bushing is greater than the outer diameter of the second mounting section. The inner diameter of the stepped bushing matches the outer diameter of the first mounting section, and the length of the smaller end of the stepped bushing is less than the length of the hardened section.

[0018] Compared with the prior art, the technical solutions of the embodiments of the present invention have beneficial effects.

[0019] For example, in the spring tube and its assembly method of the present invention, the inner tube, spring and outer tube are all assembled based on the assembly liner and the stepped bushing, ensuring that the inner tube, spring and outer tube are reliably installed coaxially. The inner tube includes an intermediate section and a hardened section disposed at at least one end of the intermediate section and connected to the intermediate section. The end of the hardened section connected to the intermediate section is sleeved on the outside of the intermediate section and partially overlaps with the intermediate section, and a step is formed on the inner wall of the hardened section. When the hardened section of the spring tube is connected to the rigid metal part, the rigid metal part is covered by the hardened section and abuts at the step, so that the inner wall of the rigid metal part is flush with the inner wall of the inner tube, making the inner wall of the blood flow channel smooth and flat, reducing the risk of blood damage and hemolysis.

[0020] For example, a second heat-shrink tubing is installed over the outer tube for heat shrinking, which allows the inner and outer tubes to be fused together at the overlap. At the same time, the pressure from the heat shrinking of the second heat-shrink tubing presses the outer tube and spring tightly against the inner tube, ensuring a tight fit between the inner tube, spring, and outer tube, thus guaranteeing the stability of the spring tube and minimizing the outer diameter of the spring tube as much as possible.

[0021] For example, an assembly liner and a stepped bushing are provided. The assembly liner includes a first mounting section, a second mounting section, and a third mounting section connected coaxially in sequence. The outer diameters of the first mounting section, the second mounting section, and the third mounting section increase sequentially. The steps between the second mounting section and the third mounting section or the steps of the stepped bushing are used to form the steps on the inner wall of the hardened section during hot melting. At the same time, the design of the steps facilitates the removal of the stepped bushing and the assembly liner. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the spring tube in an embodiment of the present invention; Figure 2 This is a cross-sectional view of the end of the spring tube in an embodiment of the present invention; Figure 3 This is a schematic diagram of the assembled core structure in an embodiment of the present invention; Figure 4 This is a sectional view of the stepped bushing in an embodiment of the present invention; Figure 5 This is a schematic diagram of the assembly of the middle section, the reinforcing section, and the stepped bushing into the assembly core structure in an embodiment of the present invention; Figure 6 This is a cross-sectional view of the middle section distal end and the reinforcing section assembled into the lining core in an embodiment of the present invention; Figure 7 This is a schematic diagram of the application of the spring tube in an embodiment of the present invention; Figure 8 This is a simulated total pressure cloud diagram of a smooth flow channel in an embodiment of the present invention; Figure 9 It is the total pressure cloud diagram for simulating stepped flow channels in existing technology; Figure 10This is a cloud map of the hemolysis index simulated in a smooth flow channel in an embodiment of the present invention; Figure 11 It is a cloud map of the hemolysis index in the stepped flow channel simulation of existing technology.

[0023] In the picture: Spring tube; 110-Inner layer tube; 111-Middle section; 112-Hardened section; 120-Spring; 130-Outer layer tube; 140-Developing ring; 200 - Assembly tooling; 210 - Assembly liner; 211 - First mounting section; 212 - Second mounting section; 213 - Third mounting section; 220 - Step bushing; 300 - Imported bridle; 400 - Pump casing. Detailed Implementation

[0024] To make the objectives, features, and beneficial effects of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It is to be understood that the specific embodiments described below are merely for explaining the present invention and are not intended to limit the present invention. Furthermore, the same or similar reference numerals may be used in the drawings to refer to the same or similar elements in different embodiments, and descriptions of the same or similar elements in different embodiments, as well as descriptions of prior art elements, features, effects, etc., may be omitted.

[0025] Reference Figure 1 and Figure 2 As shown, the present invention provides a spring tube 100, comprising an inner tube 110, a spring 120, and an outer tube 130 arranged sequentially from the inside to the outside. The inner tube 110 includes a middle section 111 and a hardened section 112 disposed at at least one end of the middle section 111 and connected to the middle section 111. The end of the hardened section 112 connected to the middle section 111 is sleeved on the outside of the middle section 111 and partially overlaps with the middle section 111. A step is formed on the inner wall of the hardened section 112. The spring 120 is sleeved on the outside of the inner tube 110 and at least covers the middle section 111. The outer tube 130 is sleeved on the outside of the spring 120 and covers the middle section 111 and the hardened section 112. The outer tube 130 overlaps with the hardened section 112.

[0026] Specifically, overlapping connection refers to the connection of overlapping parts of two components into one unit.

[0027] A step is formed on the inner wall of the hardened section 112. When the hardened section 112 of the spring tube 100 is connected to the rigid metal part, the rigid metal part is covered by the hardened section 112 and abuts at the step, so that the inner wall of the rigid metal part is flush with the inner wall of the inner tube 110, making the inner wall of the blood flow channel smooth and flat, reducing the risk of blood damage and hemolysis.

[0028] Specifically, the inner wall of the hardened section 112, which is not connected to the intermediate section 111, is provided with a knurled or threaded structure that matches the rigid metal part, thereby increasing the connection strength when connected to the rigid metal part.

[0029] In some embodiments, the length of the hardened segment 112 is 4mm-5mm, and the length of the middle segment 111 is 60mm-62mm; the length of the overlap connection between the hardened segment 112 and the middle segment 111 is 1mm-2mm.

[0030] In some embodiments, the hardness range of the hardened segment 112 is 60D-75D, the hardness range of the middle segment 111 is 80A-92A, and the material of both the hardened segment 112 and the middle segment 111 is TPU.

[0031] Specifically, the materials of the hardened segment 112 and the intermediate segment 111 can also be other medical polymer materials.

[0032] Specifically, spring 120 is made of nickel-titanium wire.

[0033] In some embodiments, a developing ring 140 is sleeved at the middle position outside the middle section 111, and the developing ring 140 is located between the middle section 111 and the spring 130.

[0034] Reference Figures 3 to 6 As shown, an embodiment of the present invention provides a method for assembling a spring tube.

[0035] Specifically, the assembly method includes the following steps: a. Provide assembly fixture 200, which includes assembly liner 210 and step bushing 220; b. Provide intermediate section 111 and fit intermediate section 111 onto the outside of assembly liner 210; c. Provide a hardened section 112, which is fitted onto the outside of the proximal end of the assembled liner 210, and a portion of the hardened section 112 is fitted onto the outside of the proximal end of the intermediate section 111 and overlaps with the proximal end of the intermediate section 111. d. The step bushing 220 is fitted onto the outside of the near end of the assembled liner 210, and the end of the step bushing 220 with the smaller outer diameter is inserted between the hardened section 112 and the assembled liner 210. The inner wall of the hardened section 112 forms a step at the contact point with the end of the step bushing 220. e. Weld the hardened section 112 and the intermediate section 111 at the overlap; f. Provide a spring 120 and fit the spring 120 around the middle section 111; g. Provide an outer tube 130, cover the inner tube 110 on which the spring 120 is sleeved with the outer tube 130, and weld the outer tube 130 and the inner tube 110 together. h. Pull out the step bushing 220, remove the assembly core 210 from the inner tube 110, and complete the assembly of the spring tube 100.

[0036] The inner tube 110, spring 120 and outer tube 130 are all assembled based on the assembly core 210 and stepped bushing 220 to ensure that the inner tube 110, spring 120 and outer tube 130 are reliably installed coaxially.

[0037] In some embodiments, the assembled liner 210 includes at least a first mounting section 211, a second mounting section 212, and a third mounting section 213 coaxially connected in sequence, with the outer diameters of the first mounting section 211, the second mounting section 212, and the third mounting section 213 increasing sequentially; the length of the second mounting section 212 is equal to or slightly greater than the length of the intermediate section 111, and in step b, the intermediate section 111 is fitted onto the second mounting section 212 of the assembled liner 210.

[0038] In some embodiments, the length of the third mounting segment 213 is less than the length of the hardening segment 112. The hardening segment 112 consists of two segments respectively disposed at the two ends of the intermediate segment 111 and connected to the intermediate segment 111. Step b further includes providing the hardening segment 112, fitting the hardening segment 112 onto the third mounting segment 213 of the assembled liner 210 and partially located in the second mounting segment 212, forming a step on the inner wall of the hardening segment 112 at the connection between the second mounting segment 212 and the third mounting segment 213, fitting the intermediate segment 111 onto the second mounting segment 212 of the assembled liner 210, such that the distal end of the intermediate segment 111 is disposed inside the hardening segment 112 and partially overlaps with the hardening segment 112.

[0039] In some embodiments, the outer diameter of the smaller end of the stepped bushing 220 is greater than the outer diameter of the second mounting section 212, the inner diameter of the stepped bushing 220 matches the outer diameter of the first mounting section 211, and the length of the smaller end of the stepped bushing 220 is less than the length of the hardened section 112. In step d, the stepped bushing 220 is fitted onto the outside of the first mounting section 211 of the assembled liner 210, and the smaller end of the stepped bushing 220 is inserted between the hardened section 112 and the assembled liner 210.

[0040] Specifically, the outer diameter of the smaller end of the step bushing 220 matches the outer diameter of the third mounting section 213.

[0041] In some embodiments, step e includes: providing a first heat shrink tubing, covering the hardened section 112 and the intermediate section 111 with the first heat shrink tubing, performing heat shrinking, and removing the first heat shrink tubing after the hardened section 112 and the intermediate section 111 are fused at the overlap; achieving fusion of the hardened section 112 and the intermediate section 111 at the overlap, such that the inner wall of the hardened section 112 forms a step at the contact point with the end of the stepped bushing 220, and the inner wall of the hardened section 112 forms a step at the connection point between the second mounting section 212 and the third mounting section 213; simultaneously pressing the inner tube 110 to the assembly liner 210 by the pressure of the heat shrinking of the first heat shrink tubing; so that the inner tube 110 and the assembly liner 210 are tightly fitted together.

[0042] In some embodiments, before step f, the method further includes: providing a developing ring 140 and fitting the developing ring 140 into the middle position outside the middle segment 111; In some embodiments, step g includes: providing a second heat shrink tube, sleeve the second heat shrink tube over the outer tube 130, heat shrinking it, and removing the second heat shrink tube after the inner tube 110 and the outer tube 130 are fused at the overlap; achieving fusion of the inner tube 110 and the outer tube 120 at the overlap, while pressing the outer tube 130 and the spring 120 to the inner tube 110 by the pressure of the heat shrinking of the second heat shrink tube; making the inner tube 110, the spring 120 and the outer tube 130 fit tightly together, ensuring the stability of the spring tube 100, and minimizing the outer diameter of the spring tube 100 as much as possible.

[0043] In some embodiments, step h is followed by bending and shaping the assembled spring tube 100.

[0044] Reference Figures 2 to 6 As shown, this embodiment of the invention also provides an assembly fixture for assembling a Bourdon tube. The assembly fixture 200 includes an assembly core 210 and a stepped bushing 220. The assembly core 220 includes a first mounting section 211, a second mounting section 212, and a third mounting section 213 coaxially connected in sequence. The outer diameters of the first mounting section 211, the second mounting section 212, and the third mounting section 213 increase sequentially. The length of the second mounting section 212 is equal to or slightly greater than the length of the intermediate section 111, and the length of the third mounting section 213 is less than the length of the hardened section. The length of the step bushing 220 is greater than the outer diameter of the second mounting section 212. The inner diameter of the step bushing 220 matches the outer diameter of the first mounting section 211. The length of the end with the smaller outer diameter of the step bushing 220 is less than the length of the hardened section 112. The step is formed on the inner wall of the hardened section 112 during hot melting through the step between the second mounting section 212 and the third mounting section 213 or the step of the step bushing 220. At the same time, the design of the step facilitates the removal of the step bushing 220 and the assembly core 210.

[0045] See Figure 7In actual use, the spring tube 100 is connected to the inlet tap 300 by the hardened section 112 at the far end and to the pump housing 400 by the hardened section 112 at the near end, so that the inner wall of the inner tube 110 is smoothly connected to the inlet tap 300 and the inner wall of the pump housing 400.

[0046] Figure 8 This is a simulated total pressure cloud diagram of a smooth flow channel in an embodiment of the present invention; Figure 9 It is the total pressure cloud diagram for simulating stepped flow channels in existing technology; Figure 10 This is a cloud map of the hemolysis index simulated in a smooth flow channel in an embodiment of the present invention; Figure 11 It is a cloud map of the hemolysis index in the stepped flow channel simulation of existing technology.

[0047] See Figures 8-11 A comparative experiment was conducted between the smooth flow channel formed by the hardened section 112 of the spring tube 100 in this embodiment of the invention and the rigid metal part, and the stepped flow channel formed by the spring tube and the rigid metal part in the prior art. Under the same boundary conditions: inlet mass flow rate 0.07943 kg / s, total temperature 310 K; outlet average static pressure 10 mmHg, the experimental results are shown in Table 1 below: Table 1 Comparison of parameters between stepped flow channels and smooth flow channels

[0048] The comparison results above show that, compared with the stepped flow channel, the smooth flow channel reduces the hemolysis index by 12.36% and the total pressure loss by 2.47%, significantly reducing the risk of blood damage and hemolysis.

[0049] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the invention, even when only a single embodiment is described with respect to a particular feature. The feature examples provided in this disclosure are intended to be illustrative and not limiting, unless otherwise stated. In practice, one or more technical features of the dependent claims may be combined with the technical features of the independent claims as needed and where technically feasible, and may be derived from the technical features of the respective independent claims in any suitable manner rather than solely by the specific combinations listed in the claims.

[0050] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A spring tube, characterized in that, The device includes an inner tube, a spring, and an outer tube arranged sequentially from the inside out. The inner tube includes a middle section and a hardened section disposed at at least one end of the middle section and connected to the middle section. The end of the hardened section connected to the middle section is sleeved outside the middle section and partially overlaps with the middle section. The inner wall of the hardened section has a step. The spring is sleeved outside the inner tube and at least covers the middle section. The outer tube is sleeved outside the spring and covers the middle section and the hardened section. The outer tube overlaps with the hardened section. In this process, the intermediate section is fitted over the assembled liner, the hardened section is fitted over the proximal end of the assembled liner, and a portion of the hardened section is fitted over the proximal end of the intermediate section, overlapping with the proximal end of the intermediate section. A stepped bushing is fitted over the proximal end of the assembled liner, and the smaller outer diameter end of the stepped bushing is inserted between the hardened section and the assembled liner. A step is formed on the inner wall of the hardened section at the contact point with the end of the stepped bushing. The step is solidified by fusing the hardened section and the intermediate section at the overlap.

2. The spring tube as described in claim 1, characterized in that, The length of the hardened section is 4mm-5mm, and the length of the middle section is 60mm-62mm; the overlap between the hardened section and the middle section is 1mm-2mm.

3. The spring tube as described in claim 1, characterized in that, The hardness range of the hardened section is 60D-75D, and the hardness range of the intermediate section is 80A-92A. Both the hardened section and the intermediate section are made of TPU.

4. The spring tube as described in claim 1, characterized in that, A developing ring is fitted at the middle position outside the middle section, and the developing ring is located between the middle section and the spring.

5. A method for assembling a spring tube as described in any one of claims 1-4, characterized in that, The spring tube includes an inner tube, a spring, and an outer tube arranged sequentially from the inside to the outside. The inner tube includes a middle section and a hardened section disposed at at least one end of the middle section and connected to the middle section. The assembly method includes the following steps: Step a: Provide assembly fixtures, which include assembly liner and step bushing; Step b: Provide an intermediate section and fit the intermediate section onto the assembled liner core; Step c: Provide a hardening segment, and fit the hardening segment onto the outside of the proximal end of the assembled liner, such that a portion of the hardening segment fits onto the outside of the proximal end of the intermediate segment and overlaps with the proximal end of the intermediate segment; Step d: Place the stepped bushing on the outside of the proximal end of the assembled liner, and insert the smaller outer diameter end of the stepped bushing between the hardened section and the assembled liner. Step e: Weld the hardened segment and the intermediate segment together at the overlap. Step f: Provide a spring and fit the spring onto the outside of the middle section; Step g: Provide an outer tube, cover the inner tube on which the spring is sleeved with the outer tube, and weld the outer tube and the inner tube together; Step h: Remove the stepped bushing and remove the assembled liner from the inner tube to complete the spring tube assembly.

6. The assembly method as described in claim 5, characterized in that, The assembled liner includes at least a first mounting section, a second mounting section, and a third mounting section connected coaxially in sequence, with the outer diameters of the first mounting section, the second mounting section, and the third mounting section increasing sequentially; the length of the second mounting section is equal to or slightly greater than the length of the intermediate section, and in step b, the intermediate section is fitted onto the second mounting section of the assembled liner.

7. The assembly method as described in claim 6, characterized in that, The length of the third mounting section is less than the length of the hardening section. The hardening section consists of two sections respectively located at both ends of the intermediate section and connected to the intermediate section. Step b further includes providing the hardening section, fitting the hardening section onto the third mounting section of the assembled liner and partially located in the second mounting section, fitting the intermediate section onto the second mounting section of the assembled liner, such that the distal end of the intermediate section is located inside the hardening section and partially overlaps with the hardening section.

8. The assembly method as described in claim 6, characterized in that, The outer diameter of the smaller end of the stepped bushing is greater than the outer diameter of the second mounting section. The inner diameter of the stepped bushing matches the outer diameter of the first mounting section. The length of the smaller end of the stepped bushing is less than the length of the hardening section. In step d, the stepped bushing is fitted onto the outside of the first mounting section of the assembled liner, and the smaller end of the stepped bushing is inserted between the hardening section and the assembled liner.

9. The assembly method as described in claim 5, characterized in that, Step e includes: providing a first heat shrink tubing, wrapping the hardened section and the intermediate section with the first heat shrink tubing, performing heat shrinking, and removing the first heat shrink tubing after the hardened section and the intermediate section are fused together at the overlap.

10. The assembly method as described in claim 5, characterized in that, Before step f, the method further includes: providing a developing ring and fitting the developing ring into the middle position outside the middle section.

11. The assembly method as described in claim 5, characterized in that, Step g includes: providing a second heat shrink tube, sleeve the second heat shrink tube over the outer tube, heat shrinking it, and removing the second heat shrink tube after the inner tube and the outer tube are fused together at the overlap.

12. The assembly method as described in claim 5, characterized in that, Step h is followed by bending and shaping the assembled spring tube.

13. An assembly fixture for the assembly method of the spring tube according to any one of claims 5 to 12, characterized in that, The assembly includes an assembled core and a stepped bushing. The assembled core comprises a first mounting section, a second mounting section, and a third mounting section coaxially connected in sequence. The outer diameters of the first, second, and third mounting sections increase sequentially. The length of the second mounting section is equal to or slightly greater than the length of the intermediate section, and the length of the third mounting section is less than the length of the hardened section. The outer diameter of the smaller end of the stepped bushing is greater than the outer diameter of the second mounting section. The inner diameter of the stepped bushing matches the outer diameter of the first mounting section, and the length of the smaller end of the stepped bushing is less than the length of the hardened section.

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