GB2172642A

GB2172642A - Sealing strip

Info

Publication number: GB2172642A
Application number: GB08531729A
Authority: GB
Inventors: Trevor Royston Tuckley; Harold William Edward Pike
Original assignee: Silent Channel Products Ltd
Current assignee: Silent Channel Products Ltd
Priority date: 1985-03-21
Filing date: 1985-12-24
Publication date: 1986-09-24
Also published as: GB2172642B; GB8531729D0

Abstract

The strip structure (10) is intended for clamping on a flange and has a channel defined by a base (12) and two opposed side walls (13, 14); wherein one (14) of the side walls has two or more projections (17 and 18) each having, a head region (21, 22) having an arcuate surface (23, 24), and a neck region (19, 20), in such that an attempt to remove the strip structure from the flange causes each projection (17, 18) to roll into greater interference with the flange, thereby increasing resistance to the removal of the flange; and wherein the other side wall (13) is provided with an elongate limb (27> and an inward projection (32) which can be accommodated within a recess (30) of limb (27), again to resist removal of the strip from the flange. <IMAGE>

Description

SPECIFICATION Strip structure intended for clamping on a flange This invention relates to a strip structure intended to be clamped securely on a flange or like member.

It is well known to provide channel-shaped strip structures intended to be clamped on a flange or like member. When used for clamping over a flange, such strip structures are often referred to as flange finishers.

Such strip structures have a channel defined by a base and two opposing side walls, which constitute a body which may be formed of a suitable rubber material or a suitable plastics material. To give any desired extra rigidity to the body it is conventional for a core to be embedded in the body, which core is usually formed of a metal.

With a view to resisting accidental removal of the strip structure from a flange, strip structures are usually provided on opposing side walls with inwardly directed limbs which act rather like a barb. Thus, when the strip structure is forced onto a flange, the limbs are caused to be deflected laterally and to be moved slightly towards the base of the channel, but, when an attempt is made to remove the strip structure from the flange, the action of the limbs pressing on the flange and their general disposition tends to prevent such removal.

It will be appreciated that with strip structures to be used on motor vehicles, it is generally desired for the force required to remove the strip structure from a flange to be considerably greater than the force required to fit the strip structure to the flange. With a typical known strip structure it was found that the ratio of the force required to remove the strip structure from the flange to the force required to clamp the strip structure to the flange was about 3.5:1 in the case of the flange having a thickness of 1.5mm, and about 2.4:1 in the case of the flange having a thickness of 2.5mm.

The need to provide strip structures which can be fitted to flanges relatively easily and yet which are strongly resistant to accidental removal, resulted in the development of strip structures in accordance with the embodiments illustrated in Figs. 1 to 3 of our British Patent Application No. 8516970, which is directed to a strip structure intended for clamping engagement on a flange or like member, the strip structure having a channel defined by a base and two opposed side walls, each side wall being integrally provided with an elongate limb directed inwardly and towards the base such that the limbs abut at their free end regions; wherein that face of each limb which faces the corresponding face of the other limb is straight or substantially straight over a portion of the limb in the region of the free end;; wherein the side walls are also each provided with an inward projection which is nearer the base of the channel than is the root of the limb; and wherein each of the limbs is provided on that face which faces the side wall with a recess in which the projection may be accommodated; the arrangement being such that, in use, when the strip structure is being clamped on a flange or like member, the flange causes the limbs to be moved apart, with the projections being accommodated in the corresponding recesses, whereby the clamping may be effected without undue force, but, when an attempt is made to remove the strip structure from the flange, the free end regions of the limbs grip the flange and the limbs are restrained from undue movement towards the open end of the channel by the interaction of the projections and the limbs in the region of the recesses of the latter, the configuration of the limbs and the effect of said interaction being such that considerably more force is required to remove the strip structure from the flange than is required to clamp the strip structure on the flange.

Preferably each limb of the strip structue of British Patent Application No. 8516970 has a length, as measured along the face which faces the corresponding face of the other limb, which exceeds the width of the channel at the point where the root of the limb projects from its respective side wall. Also, preferably the limbs are formed, on at least those surface regions which face the opposing limb, from a polished plasticised polyvinyl chloride material.

The strip structures in accordance with British Patent Application No. 8516970 have a high ratio of the force required to remove the strip structure from a flange to the force required to fit the strip structure on a flange.

The results obtainable in practice with painted flanges were impressive.

Another style of strip structure which has been found to give good results in practice is that disclosed and claimed in our British Patent Application No. 8507432, which is directed to a strip structure intended for attachment to a flange, which strip structure comprises a generally U-shaped body in which is embedded a reinforcing member, the body having a base region and two opposed side wall regions, which between them define a channel intended for accommodating a flange, each side wall region being provided with at least one projection which projects into the channel and is inclined towards the base region, wherein at last one of the projections present in the strip structure is a rolling projection having, as seen in a cross-section through the strip structure, a free head region and a neck region, the head region being enlarged relative to the neck region and the head region having an arcuate surface in that portion intended to abut said flange when the latter is accommodated with the channel, the arrangement being such that, when a flange is accommodated in the channel with the projections abutting the flange, an attempt to remove the strip structure from the flange causes each rolling projection to tend to roll into greater interference with the flange, thereby increasing resistance to the removal of the flange.

Preferably, but not necessarily, each side wall region of the body of the strip structure of British Patent Application No. 8507432 is provided with a plurality of projections, generally two or three projections. By having a plurality of projections the flange finisher can be secured on a flange in a stable manner without any lateral wobbling. Moreover, preferably, but not necessarily, the or each projection from one side wall region is a rolling projection of the type referred to above whereas the or each projection from the other side wall region is of a different configuration, for example one which tapers towards its free end or is generally parallel on those sides leading to the free end.Although it is possible for rolling projections to be provided on both side wall regions of the body, it is preferred for there to be two or three rolling projections on one side wall region of the body and reasonably rigid projections of a different configuration on the other side wall region of the body. This has the advantage that the nonrolling projections serve as reasonably firm points which bear on one face of the flange, whereas the rolling projections, with their interference action, are then free to act on the other face of the flange.

The embodiment illustrated in Fig. 4 of our British Patent Application No. 8516970 shows the case in which each limb has at its free end region an enlarged head of which a proximal part is formed as a rolling key capable, in use, when the strip structure is clamped on a flange, of interacting with the respective projection to resist removal of the strip structure from the flange. Such a rolling key can be regarded as an optional minor rolling key, being minor in dimension to the relatively major rolling key or keys which are at the heart of the invention covered in our British Patent Application No. 8507432.

When a strip structure of the type illustrated in Fig. 4 of British Patent Application No.

8516970 was used on a flange covered with a fabric formed from a plastics material, the resistance to removal was not as marked as when that strip structure was applied to a painted flange. Nonetheless, the degree of resistance was still considerable and was still greater than that required for certain applications associated with motor vehicles.

It was felt that it would be desirable to provide a strip structure which could be applied to both painted flanges and flanges covered with a plastics fabric (such as a vehicle headlining), and which would have a good degree of resistance to removal by accident.

According to the present invention, there is provided a strip structure intended for clamping engagement on a flange or like member, the strip structure having a channel defined by a base and two opposed side walls; wherein one of the side walls is provided with two or more rolling projections which project into the channel and are inclined towards the base, the rolling projections each having, as seen in a cross-section through the strip structure, a free head region and a neck region, the head region being enlarged relative to the neck region and the head region having an arcuate surface in that portion intended to abut the flange when the latter is accommodated within the channel, the arrangement being such that, when a flange is accommodated in the channel with the rolling projections abutting the flange, an attempt to remove the strip structure from the flange causes each rolling projection to tend to roll into greater interference with the flange, thereby increasing resistance to the removal of the flange; wherein the other side wall is integrally provided with an elongate limb directed inwardly and towards the base, with that face of the elongate limb which faces the said one side wall being straight or substantially straight over a portion of the limb in the region of its free end; wherein the said other side wall is also provided with an inward projection which is nearer the base of the channel than is the root of the elongate limb; and wherein the elongate limb is provided on that face which faces said other side wall with a recess in which the inward projection may be accommodated, the arrangement being such that, in use, when the strip structure is being clamped on a flange or like member, the flange causes the elongate limb to be moved towards said other side wall, with the inward projection being accommodated in the recess whereby the clamping may be effected without undue force, but, when an attempt is made to remove the strip structure from the flange, the free end region of the elongate limb grips the flange and the elongate limb is restrained from undue movement towards the open end of the channel by the interaction of the inward projection and the elongate limb in the region of the recess of the latter, the configuration of the elongate limb and the effect of said interaction being such that considerably more force is required to remove the strip structure from the flange than is required to clamp the strip structure on the flange.

As with conventional strip structures which serve as flange finishers, the strip structure of the present invention can have, but does not need to have, a sealing element attached to the exterior of the body (i.e. the base and side walls) of the strip structure. Such an arrangement is often employed in the region of the doors of automobile bodies, with the strip structure being secured to a flange and the sealing element forming a suitable seal between the door and the door frame.

The strip structures according to the present invention can have any suitable body, and it is not necessary for the body to have a metal core, although this is nowadays conventional in practice as the core can resist any tendency of the two side walls defining the channel to move apart during an attempt to remove the strip structure from a flange.

In one embodiment of the present invention, the recess in the elongate limb is rather large compared with the magnitude of the inward projection, and the free end region of the limb increases in thickness in the direction from the free end towards the root, so that a head portion, rather like half an arrowhead, is present in the free end region of the limb. It is that end of the arrowhead portion nearer the root which abuts the inward projection, when the strip structure is fitted to a flange and an attempt is made to remove the strip structure from the flange.

Preferably, in the manner disclosed for the first time in Fig. 4 of British Patent Application No. 8516970, the elongate limb has an enlarged region of which a proximal part is formed as a rolling key capable, in use, when the strip structure is clamped on a flange, of interacting with the inward projection to resist removal of the strip structure from the flange.

Preferably the inward projection has a camming face so that, with the elongate limb adhering to the flange, any attempt to cause the flange to be removed tends to cause the elongate limb to be moved towards the open end of the channel but, when this happens, the camming action of the camming face of the inward projection urges the elongate limb even more tightly against the flange, thereby tending to increase the resistance to removal of the strip structure from the flange.

The body and the elongate limb and rolling projections of the strip structure according to the present invention are preferably formed of polyvinyl chloride, but they could be formed of a rubber material, such as a styrene butadiene rubber, and the body portion of the strip structure could have a hardness of 70 Shore, with the elongate limb and rolling projections having a hardness of 60 Shore. If desired a sponge sealing element formed from, for instance, an ethylene/propylene/diene monomer terpolymer (EPDM) could be secured to the exterior of the base or of one of the two side walls. Rather than form.the body (including the elongate limb and rolling projections) from styrene butadiene rubber, the body together with any sealing element could be formed from the ethylene/propylene/diene monomer terpolymer.

When both the body (including the elongate limb and rolling projections) and any sealing element are formed of a single material, preferably polyvinyl chloride, the strip structure could be formed during a single extrusion operation.

In a second, preferred, embodiment of the present invention, the recess in the elongate limb is smaller than in the first embodiment, but again the inward projection has a camming surface so that, when the strip structure is fitted on a flange, with the long straight edge region of the elongate limb abutting one side of the flange, any attempt to remove the strip structure from the flange causes a region of the elongate limb defining part of the recess to abut the camming face of the inward projection, thereby tending to increase the resistance to the removal of the strip structure from the flange.

In practice, when it is expected that flanges having a thickness of from 1.5 to 2.5mm are to be fitted with the strip structure, the width of the elongate limb other than in the region of the recess, and the width of the rolling projections is prefereably such that the elongate limb, rolling projections and the flange occupy the great majority of the width of the channel. Although the inward projection certainly assists in encouraging the elongate limb to grip the flange more firmly, nonetheless even if the inward projection was very small, the magnitude and configuration of the elongate limb can be such that the elongate limb has a good gripping effect on the flange.Often the body, in which the metal core (when present) is embedded, is formed of a polyvinyl chloiide, or a nitrile polyvinyl chloride blend, although many other different materials can be used to construct the body, including the elongate limb and rolling projections.

It has been stated above that the length of the elongate limb, as measured in the manner indicated above, preferably exceeds the width of the channel at the point at which the root of the elongate limb is affixed to the said other side wall of the channel. Preferably the length of the elongate limb to the width of the channel exceeds the ratio 1.1:1; more preferably the ratio of the length of the limb to the width of the channel exceeds the ratio 1.2:1, good results in particular being obtained when the ratio of the length of the limb to the width of the channel exceeds 1.3:1, or more preferably exceeds 1.4:1, even reaching approximately 1.5:1.

If desired, the elongate limb is formed, or the rolling projections are formed, on at least those surface regions which face the opposing side wall, from a polished plasticised polyvinyl chloride material; the arrangement being such that, in use, when an attempt is made to remove the strip structure from a smooth flange on which it is clamped, the polished plasticised polyvinyl chloride nature of those surface regions enhances the grip on the flange, whereby considerably more force is required to remove the strip structure from the flange than is required to clamp the strip structure on the flange.

As regards the polished plasticised polyvinyl chloride material, this can exist as a surface region only of the elongate limb and/or rolling projections; alternatively, the whole or substantially the whole elongate limb and/or rolling projections can be formed from this material. It is interesting to observe that the good retention results obtainable with a strip structure in accordance with the present invention, can be enhanced when the polished plasticised polyvinyl chloride surface regions of the elongate limb and rolling projections are provided.

Preferably, the arcuate surface of the head region of each rolling projection is involute.

Sometimes, at least part of the external surface of the strip structure is covered with a flock.

The strip structure may include a core embedded within the base and side walls of the strip structure.

The strip structure may be one which, when being fitted to and removed from a flange having a thickness of 2.5mm, has a ratio exceeding 7:1 in respect of the ratio of the force required to remove the strip structure from the flange to the force required to push the strip structure onto the flange.

Preferably the free end region of the elongate limb is provided with a stabilising fin intended, in use, when a flange causes the elongate limb to move towards the said other side wall, to abut that side wall.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a cross-section through one embodiment of a strip structure in accordance with the present invention; and Figure 2 is a cross-section through the same embodiment as shown in Fig. 1, but with the strip structure fitted on a flange.

Referring first to Fig. 1, the strip structure generally indicated by the reference numeral 10 comprises a body generally indicated by the reference numeral 1 t which has a base 12 and two almost parallel side walls 13, 14.

Embedded in the body 11 is a metal reinforcing core 15. The body 11 is generally channel-shaped.

Projecting externally from the corner region between the base 12 and the side wall 13 is a sealing portion 16 but; as mentioned above, this is an optional feature.

The side wall 14 is provided with two rolling projections 17 and 18 which face towards the opposite side wall 13.

The rolling projections 17 and 18 have respective neck regions 19 and 20 which lead to enlarged head regions 21 and 22, respectively. The head regions 21 and 22 have respective arcuate surfaces 23 and 24 which can be, but need not be, involute in configuration. It is these arcuate surfaces 23 and 24 which, in use of the strip structure, are to abut one face of a flange (not shown in Fig.

1) which is inserted into the channel defined by the base 12 and side walls 13 and 14.

Other surface regions 25 and 26 of the head portions 21 and 22 are generally rectilinear but, as these surfaces will not abut the flange their configuration is not of significance, except that these surface regions 25 and 26 of the head portions 21 and 22 need to be of such a configuration as to allow the rolling projections 17 and 18 to pivot anti-clockwise (in Fig. 1) about the neck portions 19 and 20 when a flange is being introduced into the aforementioned channel.

Projecting from the side wall 13 inwardly and towards the base 12 is an elongate limb 27. The limb 27 has a shank portion 28 in that portion of its length nearer the point at which it is attached to the side wall 13. The shank portion 28 leads to a head portion 29 which abuts the innermost rolling projection 17. The shape of the shank portion 28 and the head portion 29 is such as to define a recess 30, the head portion 29 having a barblike portion 31 directed towards the side wall 13.

Also projecting from the side wall 13 inwardly into the interior of the channel is an inward projection 32. The projection 32 has a camming face 33 for the purpose indicated below.

Also, projecting from the head portion 29 of the limb 27 is a stabilising fin 34 directed towards the side wall 13.

When a fabric covered flange 40 (in Fig. 2) is to be fitted with a strip structure in accordance with Fig. 1, the flange is moved into the channel defined by the base 12 and side walls 13, 14 and, as the flange advances, it pushes aside the elongate limb 27 and the rolling projections 17 and 18. This is possible because the inward projection 32 is accommodated within the recess 30. Also, as indicated above, the rolling projections 17 and 18 flex about their neck regions 19 and 20.

Prior to the flange 40 entering the channel, the head region 29 of the elongate limb 27 abutted the innermost rolling projection 17.

Now, with the flange 40 inserted fully into the channel, the elongate limb 27 and rolling projection 17 are forced apart, and the head portions 29, 21 and 22 abut and adhere to the flange. This is because the elongate limb 27 and rolling projections 17 and 18 are generally tactile.

When the flange is fully inserted in the channel, the barb-like portion 31 of the head portion 29 of the limb 27 is against or almost against the side wall 13 and is near the inward projection 32.

Also, the stabilising fin 34 abuts the side wall 13 and reduces the likelihood of the strip structure 10 wobbling or rocking on the flange.

As soon as any attempt is made to remove the strip structure 10 from the flange, then, in view of the tendency of the head portion 29 to remain stationary with respect to the flange, it can be apreciated that any tendency of the elongate limb 27 to be moved towards the open end of the channel causes the barblike portion 31 to abut the camming face 33 of the projection 32 with the result that any such movement tends to cause the elongate limb 27 to be urged inwardly and hence even more tightly against the flange, thereby increasing the resistance to removal of the flange.

In the preferred embodiment illustrated in the drawings, the barb-like portion 31 is formed as a rolling key which, when reacting with the camming face 33 of the projection 32 rolls when any attempt is made to remove the strip structure 10 from the flange, which further enhances the removal-resistance effect.

Any attempt to remove a flange from the channel also causes the rolling projections 1 7 and 18 to tend to rotate, clockwise in Fig. 1, about their neck portions 19 and 20, which urges the head portions 21 and 22 into tighter abutment with the flange.

Although the strip structure shown in Fig. 1 can be formed of any suitable material, it is preferred to use a polyvinyl chloride; in such a case the performance of the strip structure can be enhanced, in the sense of increasing the resistance to removal of the strip structure from the flange, by forming at least the inwardly facing faces of the elongate limb 27 and of the rolling projections 17 and 18 of a polished, plasticised polyvinyl chloride material, or by forming the whole of the limb 27 and projections 17 and 18 of such material. It is well known how polyvinyl chloride can be treated to make it polished, and in the present case it has been found convenient, when the limb 27 and rolling projections 1 7 and 18 are formed of a plasticised polyvinyl chloride, to effect extrusion of those components at a higher temperature than is normally employed.

Here, it has to be appreciated that if too high a temperature is employed the heat can have a detrimental effect on the quality of the polyvinyl chloride. If, though, the temperature exceeds the normally lower, conventional, extrusion temperature the polyvinyl chloride produced- can be suitably plasticised and polished, and this is especially so when the polyvinyl chjloride is a clear polyvinly chloride.

To facilitate manufacture of the strip structure by extrusion, the strip structure is extruded with the side walls 13 and 14 slightly splayed apart, because of the positioning of those portions of the extrusion orifice which are to be responsible for creating the limb 27 and projections 17 and 18. After extrusion and curing, the strip structure can be moved through a forming machine which acts on the outside of the side walls 13 and 14 to bring them together so as to adopt the configuration shown in Fig. 1.

In the embodiment illustrated in Fig. 1, all of the body and sealing portion (but obviously excluding the metal reinforcing member 5) are formed of the same material but clearly it will be possible to form different parts of the strip structure from materials having different degrees of hardness, which is a well-established practice in- this art. Clearly, however, it is easier to form the strip structure from a single extrudable material which may be a rubber or a rubber-like synthetic material, and is preferably a polyvinyl chloride. Good results have been achieved by employing a rubber having a 65 Shore A hardness+5 , but any alternative material capable of being extruded satisfactorily may be employed, although the material should not be too hard : thus, generally the material should not have a hardness above 80 Shore A.

It has been found, in tests conducted with a strip structure like that shown in Fig. 1, that the strip structure can easily be applied to a flange but only removed therefrom with considerable difficulty.

With further regard to the arcuate faces 23 and 24, these are preferably involute, in that the projections 1 7 and 18 will be caused to maintain the same contact with the flange when the strip structure is fitted to the flange.

Claims

1. A strip structure intended for clamping engagement on a flange or like member, the strip structure having a channel defined by a base and two opposed side walls; wherein one of the side walls is provided with two or more rolling projections which project into the channel and are inclined towards the base, the rolling projections each having, as seen in a cross-section through the strip structure, a free head region and a neck region, the head region being enlarged relative to the neck region and the head region having an arcuate surface in that portion intended to abut the flange when the latter is accommodated within the channel, the arrangement being such that, when a flange is accommodated in the channel with the rolling projections abutting the flange, an attempt to remove the strip structure from the flange causes each rolling projection to tend to roll into greater interference with the flange, thereby increasing resistance to the removal of the flange; wherein the other side wall is integrally pro vided with an elongate limb directed inwardly and towards the base, with that face of the elongate limb which faces the said one side wall being straight or substantially straight over a portion of the limb in the region of its free end; wherein the said other side wall is also provided with an inward projection which is nearer the base of the channel than is the root of the elongate limb; and wherein the elongate limb is provided on that face which faces said other side wall with a recess in which the inward projection may be accommodated, the arrangement being such that, in use, when the strip structure is being clamped on a flange or like member, the flange causes the elongate limb to be moved towards said other side wall, with the inward projection being accommodated in the recess whereby the clamping may be effected without undue force, but, when an attempt is made to remove the strip structure from the flange, the free end region of the elongate limb grips the flange and the elongate limb is restrained from undue movement towards the open end of the channel by the interaction of the inward projection and the elongate limb in the region of the recess of the latter, the configuration of the elongate limb and the effect of said interaction being such that considerably more force is required to remove the strip structure from the flange than is required to clamp the strip structure on the flange.

2. A strip structure according to Claim 1, wherein the inward projection has a camming face against which, when in use an attempt is made to remove the strip structure from the flange, an enlarged region of the elongate limb abuts, in a manner such as to urge the free end region of the elongate limb into harder contact with the flange.

3. A strip structure according to Claim 1 or 2, wherein the elongate limb has a length, as measured along the face which faces the said one side wall, which exceeds the width of the channel at the point where the root of the elongate limb projects from the said other side wall.

4. A strip structure according to Claim 3, wherein the ratio of the length of the elongate limb, as measured along the face which faces the said one side wall, to the width of the channel at the point where the root of the elongate limb projects from the said other side wall exceeds 1.1:1.

5. A strip structure according to Claim 4, wherein said ratio exceeds 1.2:1.

6. A strip structure according to Claim 4, wherein said ratio exceeds 1.3:1.

7. A strip structure according to Claim 4, wherein said ratio exceeds 1.4:1.

8. A strip structure according to Claim 4, wherein said ratio is approximately 1.5:1.

9. A strip struture according to any preceding claim, wherein the elongate limb is formed, or the rolling projections are formed, on at least those surface regions which face the opposing side wall, from a polished plasticised polyvinyl chloride material; the arrangement being such that, in use, when an attempt is made to remove the strip structure from a smooth flange on which it is clamped, the polished plasticised polyvinyl chloride nature of those surface regions enhances the grip on the flange, whereby considerably more force is required to remove the strip structure from the flange than is required to clamp the strip structure on the flange.

10. A strip structure according to Claim 9, wherein the whole or substantially the whole of the elongate limb or of the rolling projections is formed of a polished, plasticised polyvinyl chloride material.

11. A strip structure according to any preceding claim, wherein the arcuate surface of the head region of each rolling projection is involute.

12. A strip structure according to any preceding claim, which includes an outwardly directed sealing part.

13. A strip structure according to any preceding claim, wherein at least part of the external surface of the strip structure is covered with a flock.

14. A strip structure according to any preceding claim, which also includes a core embedded within the base and side walls of the strip structure.

15. A strip structure according to any preceding claim, wherein the base and two side walls are formed of a polyvinyl chloride, a nitrile polyvinyl chloride blend, or a styrene butadiene rubber.

16. A strip structure according to any preceding claim, wherein the base and side walls have a Shore hardness of approximately 70 and the elongate limb and rolling projections have a Shore hardness of approximately 60.

17. A strip structure according to any preceding claim, wherein the elongate limb has an enlarged region of which a proximal part is formed as a rolling key capable, in use, when the strip structure is clamped on a flange, of interacting with the inward projection to resist removal of the strip structure from the flange.

18. A strip structure according to any preceding claim, wherein the free end region of the elongate limb is provided with a stabilising fin intended, in use, when a flange causes the elongate limb to move towards the said other side wall, to abut that side wall.

19. A strip structure according to any preceding claim, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.