Method for introducing an internal helical formation into a flexible tubular material
There is disclosed a method for introducing a helical formation ( 11 ) into a flexible tubular material ( 12 ). The material ( 12 ) is supported together with a surrounding helical former ( 13 ) so as to deform the material ( 12 ) to have a helical indentation ( 11 ) corresponding to the shape of the former ( 13 ). The material ( 12 ) is then set in that configuration and the former ( 13 ) is removed.
1. A method for introducing an internal helical formation into a flexible tubular material such that the internal helical formation is capable of conferring a helical flow on liquid flowing through the tubular material, the method comprising the steps of:
i) placing the flexible tubular material on a non-grooved mandrel, winding a thread around the material, pushing the ends of the material together so as to deform the material to have a concertinaed configuration, setting the material in that configuration, and removing the thread and the mandrel, wherein the thread is removed either before or after the material is set; and
ii) supporting the material on a mandrel having a groove, placing a helical former corresponding to the groove around the material so as to deform the material to have an internal helical formation corresponding to the shape of the groove, setting the material in that configuration in a second setting operation, and removing the former and the mandrel.
2. A method according to claim 1 , in which the material is supported in a surrounding structure together with the former.
3. A method according to claim 1 or claim 2 , in which the material is thermoplastic or thermosetting and the material is set by any one of: heat setting, chemical setting, infra-red setting and ultra-violet setting.
4. A method according to claim 1 , wherein the material is woven.
5. A method according to claim 1 , wherein the material is knitted.
6. A method according to claim 1 , in which the material is pre-tensioned during the introduction of the helical formation.
7. A method according to claim 6 , in which the material is pre-tensioned to 10% of its maximum extensibility.
8. A method according to claim 1 , in which a second material is applied to the material after the second setting operation.
9. A method according to claim 8 , wherein the former creates an indentation in the external side wall of the material and the second material is applied to the indentation.
10. A method according to claim 9 , wherein the second material overflows the indentation.
11. A method according to claim 8 , wherein the second material is a polyurethane dispersion.
12. A method according to claim 8 , wherein the second material is pressed into the tubular material such that the second material penetrates the tubular material.
13. A method according to claim 12 , wherein the second material does not penetrate the material to the internal side wall.
14. A method according to claim 13 , wherein the second material penetrates at least 50% but less than 100% into the side wall of the material.
15. A method according to claim 14 , wherein the second material penetrates 80% to 90% into the side wall.
16. A method according to claim 1 , in which a strand of a third material having a different modulus of elasticity to the tubular material is introduced into and secured in the helical formation after the setting operation.
17. A method according to claim 16 , in which the strand material comprises a monofilament.
18. A method according to claim 16 , in which the strand material comprises a multifilament strand.
19. A method according to claim 16 , in which the strand is secured by applying a coating to the tubular material.