GB2200427A

GB2200427A - Flexible ducting

Info

Publication number: GB2200427A
Application number: GB08728579A
Authority: GB
Inventors: Albert Edward David Walters
Original assignee: Flexadux Plastics Ltd
Current assignee: Flexadux Plastics Ltd
Priority date: 1986-12-06
Filing date: 1987-12-07
Publication date: 1988-08-03
Also published as: GB8728579D0

Abstract

Flexible ducting (11) formed by bending a length of plastics sheet into tubular form with overlapping edge portions (12, 13) bonded, as by adhesive, solvent or welding (14), to form a longitudinal seam (10) has a strengthening strip (15) of plastics material extending across the seam, with marginal portions (16, 17) bonded, as by adhesive, solvent or welding (18, 19) to the ducting (11) at both sides of the seam (10). Marginal welding (18, 19) preferably does not extend to the longitudinal edges (20, 21) of the strip (15), so that no bulging is caused if pressure is applied during welding, but preferably only slightly in from those edges so that they are not liable to be caught and torn by handling equipment. A strengthening strip may be similarly applied to a circumferential seam between two such lengths of flexible ducting. <IMAGE>

Description

FLEXIBLE DUCTING This invention relates to flexible ducting of the type formed from a length of plastics sheet bent into tubular form with overlapping edge portions which are bonded together to form a longitudinal seam. The overlapping edge portions are usually pressed together during bonding by welding, which can result in bulging of the plastics material along each side of the longitudinal# seam. Two or more such lengths may be overlapped at adjacent ends and be bonded together to form a circumferential seam. The seam or seams do not detract from the ability of the ducting to be flattened and folded for easy storage and transport.

Ducting produced by this method is joined to similar ducting by coupling bands to form a ventilation duct of Iny desired length for mining or tunnelling. As the length is increased the pressure has to be increased to ensure that the necessary quantity of air flows through the duct. The limiting factor is the strength of the duct and particularly the weakest part of the duct, which is the seam and which may part along the weld or along the bulging at one side or other of the-seam. The stronger the material, e.g., to withstand greater pressure, the more important becomes the strength of the joint.

To overcome this restriction it has hitherto been necessary to use a stronger, more expensive material or a larger diameter duct or to stage a plurality of fans along the duct to maintain the necessary flow.

The object of the present invention is to provide simpler means for overcoming the aforesaid restriction.

According to one aspect of the present invention, flexible ducting of the type initially defined is provided with a strip of plastics material of a width exceeding the width of the seam and marginal portions of the strip are bonded to the ducting at both sides of the seam.

The strip may be initially slack between the marginal bonds - even to the extent that the strip bulges slightly away from the seam - so that the strip only becomes loaded in use as the ducting stretches as it comes up to working pressure.

Although it adds further to the thickness of the seam, the strip of plastics material need not detract appreciab#y from the ability of the ducting to be flattened and, in particular, to be folded, even if - as is possible within the scope of the invention - the strip of plastics material is also bonded to the overlapping edge portion forming the outer part of the seam, either separately from or contiguously with either or both marginal bonds.

According to another aspect of the present invention, flexible ducting of the type initially defined is provided with a strip of plastics material of a width exceeding the width of the seam, one marginal portion of the strip is bonded to the outer overlapping edge portion, the strip extends over and beyond the edge proper of the outer overlapping edge portion, and another marginal portion of the strip is bonded to the outside of the ducting at a distance from the seam.

The strip of plastics material may have the same thickness as the length of plastics sheet (e.g., 1 to 1.5 mm each) or it may have a greater thickness or a lesser thickness, in which latter case it can still significantly increase the strength without noticeably detracting from the ability to be folded. Tests using the same thickness have shown that increases in pressure of 25% or more can be easily sustained, and using a greater thickness it may even be possible to afford a safety margin up to 188% higher than recommended working pressure.

The marginal bonding may be effected by adhesive or solvent cement but is preferably formed by welding which is effected at a lower temperature and/or lesser pressure than is used to form the seam, and the marginal welding preferably does not extend precisely to the longitudinal edges of the strip of plastics material, so that no bulging is caused if pressure is applied during welding, but preferably only slightly in from the longitudinal edges so that those edges are not liable to be caught and torn by handling equipment.

The invention is applicable equally to a circumferential seam as to a longitudinal seam.

Likewise, the invention may be employed to strengthen a seam that is sewn, secured by adhesive, or bonded by other means than welding e.g., solvent cement, provided that a sewn seam is made impervious, as by applying a sealant over and around the stitching and stitch holes, and the sealant is capable of withstanding substantially more than the working pressure.

A number of embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a fragmentary cross-section through the seam of flexible plastics ducting in accordance with the invention; Figure 2 corresponds to Figure 1 but shows a preferred embodiment of the invention; Figure 3 corresponds to Figure 2 but shows a slight modification; Figure 4 is a fragmentary cross-section through another embodiment of seam of flexible plastics ducting in accordance with the invention; Figure 5 corresponds to Figure 4 but shows the seam under load as the ducting comes up to working pressure; and Figure 6 is a fragmentary cross-section through a further embodiment of seam of flexible plastics ducting in accordance with the invention.

In all the drawings the thicknesses of the plastics material are exaggerated for ease of illustration. Also, the curvature of the plastics material indicates that all the drawings show longitudinal seams, but they would be equally applicable to circumferential seams between lengths of ducting.

In Figure 1 a longitudinal seam 18 of flexible ducting 11 of the type formed from a length of plastics sheet bent into tubular form with overlapping edge portions 12, 13 welded together (as indicated at 14) is bridged by a strip 15 of plastics material of a width exceeding the width of the seam 1~, and marginal portions 16, 17 of the strip are welded (as indicated at 18, 19) to the ducting at both sides of the seam 18. Preferably, as shown in Figure 2, the marginal welding 18, 19 does not extend precisely to the longitudinal edges 2~, 21 of the strip 15, so that no bulging is caused if pressure is applied during welding, but only slightly in from the longitudinal edges 2~, 21 so that those edges are not liable to be caught and torn by handling equipment.

As shown in Figure 3, the strip 15 may also be welded (at 22) to the overlapping edge portion 12 forming the outer part of the seam 1~, and - although not shown - may be contiguous with either or both marginal welds 18, 19.

In Figure 4 the strip 15 is initially slack between the marginal welds 18, 19 to the extent that the strip bulges slightly away from the seam 1~, so that the strip 15 only becomes loaded in use as the ducting stretches as it comes up to working pressure, as indicated by Figure 5.

In the embodiment of Figure 6 a strip 23 of plastics material of a width exceeding the width of the seam 18 has one marginal portion 24 welded (at 25) to the outer overlapping edge portion 12, the strip extends over and beyond the edge 26 proper of the edge portion 12, and another marginal portion 27 is welded (at 28) to the outside of the ducting 11 at a distance from the seam.

Claims

1. Flexible ducting formed from a length of plastics sheet bent into tubular form with overlapping edge portions which are bonded together to form a longitudinal seam, and provided with a strip of plastics material of a width exceeding the width of the seam, marginal portions of the outer strip being bonded to the ducting at both sides of the seam.

2. Flexible ducting as in Claim 1, wherein the strip is initially slack between the marginal bonds, so that the strip only becomes loaded in use as the ducting stretches as it comes up to working pressure.

3. Flexible ducting as in Claim 2, wherein the strip initially bulges slightly away from the seam.

4. Flexible ducting as in Claim 1, wherein the strip of plastics material is also bonded to the overlapping edge portion forming the outer part of the seam, either separately from or contiguously with either or both marginal bonds.

5. Flexible ducting formed from a length of plastics sheet bent into tubular form with overlapping edge portions which are bonded together to form a longitudinal seam, and provided with a strip of plastics material of a width exceeding the width of the seam, one marginal portion of the strip being bonded to the outer overlapping edge portion, the strip extending over and beyond the edge proper of the outer overlapping edge portion, and another marginal portion of the strip being bonded to the outside of the ducting at a distance from the seam.

6. Flexible ducting as in any one of Claims 1 to 5, wherein the strip of plastics material has the same thickness as the length of plastics sheet forming the ducting.

7. Flexible ducting as in any one of Claims 1 to 5, wherein the strip of plastics material has a greater thickness than the length of plastics sheet forming the ducting.

8. Flexible ducting as in any one of Claims 1 to 5, wherein the strip of plastics material has a lesser thickness than then length of plastics sheet forming the ducting.

9. Flexible ducting as in any one of Claims 1 to 8, wherein the marginal bonding is effected by adhesive-or solvent cement 18. Flexible ducting as in any one of Claims 1 to 8, wherein the marginal bonding is by welding which is effected at a lower temperature and/or lesser pressure than is used to form the seam.

11. Flexible ducting as in Claim l#, wherein the marginal welding does not extend precisely to the longitudinal edges of the strip of plastics material.

12. Flexible ducting comprising at least two lengths as in any one of Claims 1 to 11 with a circumferential seam provided with a strip of plastics material as in any one of Claims 1 to 11.

13. Flexible ducting as in any one of Claims 1 to 12, wherein the or each seam is sewn.

14. Flexible ducting as in any one of Claims 1 to 12, wherein the or each seam is secured by adhesive.

15. Flexible ducting as in any one of Claims 1 to 12, wherein the or each seam is bonded by solvent cement.

16. Flexible ducting substantially as hereinbefore described with reference to any one of Figures 1 to 3, or Figures 4 and 5, or Figure 6.