GB2228023A - Fixing sheet material - Google Patents

Abstract

A flexible membrane 23 is secured to a channel sectioned frame member 1 by securing an insert 3 in the channel so as to trap the membrane. The frame members may be the loops of a plastic greenhouse or the uprights of a fence. The membrane may be of metal. <IMAGE>

Description

Title: Fixing Sheet Material.

DESCRIPTION The present invention relates to the fixing of sheet material, especially in relation to membrane fixing for skinned structures such as polyhouses.

By membrane we mean sheet like material including such as perforate and imperforate plastics sheeting, mesh-like materials of plastics, fibre, even metal.

By structure we means anything from a simple fence like structure having two posts to multi-span 3 dimensional structures such as "polyhouses" and including a simple self incorporating planar framework.

In recent years so called "polyhouses" have established themselves especially in agricultural/horticultural applications as economical means of covering large areas of ground, providing an alternative to the traditional glasshouse, also as sheltered propagation units, even as light tight mushroom propagation units or other useful enclosures.

The structure comprises a framework which is typically made up of a series of longitudinally spaced hoops of metal linked by longitudinal runners. The hoops are covered by a skin or membrane of which plastics sheeting is typical, although a variety of different coverings are available having different stiffnesses and/or thicknesses, perforate or imperforate. The ability of such polyhouses to withstand exposure to weather, in particular windy conditions, is aided at least in part by secure and preferably taut fixing of the skinning.

Application of plastics skinning to such polyhouses calls for fixing along opposite lower longitudinal boundaries of the sheeting with the sheeting passing over.the structure, and at ends of the houses. One way of doing this is to provide a plurality of eyelets or such like along the edges through which ties are passed, but such fixing can suffer from the disadvantage of pulling out due to high point loading.

Another system has used two interengageable aluminium extrusions having cooperating male and female parts in the form of one or more longitudinal ribs designed to be received in a respective longitudinal groove and to secure the plastics membrane by trapping same between the rib and groove. A known extrusion has ribs approximately 2 mm wide and 5 mm long with grooves dimensioned to receive same as a snap-in fit for a particular thickness of membrane.

Such a known membrane fixing system suffers from several disadvantages. Firstly, the snap fitting interengagement of the two parts calls for close tolerances of those parts and dictates that different sizes of parts be used when it is required to accommodate different thicknesses of membrane.

Secondly, there is a tendency for the metal (which is unsympathetic in relation to typical membrane materials) of the two extrusions to nip through the membrane as the parts are pushed home and this creates weak spots which, under stressing of the membrane can develop into tears. Thirdly, largely as a consequence of the above disadvantages, the parts of the extrusion have to be brought together with the membrane relatively untensioned, actually slack, with the result that the fixed skin is not as taut as is preferred.

Finally, aluminium is a relatively high cost material, at least compared with steel, and so sections are made as small as practicable to keep cost within reason and hence the sections are of relatively low strength so that they have to be used in conjunction with a suitable reinforcement, usually secured to a longitudinal runner of steel extending between hoops.

This adds to the expense.

It is an aim of the present invention to provide for sheet fixing which overcomes the aforementioned problems and in doing so to provide for improved flexibility in fixing sheet material of different degrees of flexibility.

According to one aspect of the invention there is provided a member for retaining sheet material which may be perforate or imperforate and which exhibits at least some degree of deflection/flexibility, the member comprising an elongate channel member preferably of sufficient depth and rigidity to be self supporting for most applications, conveniently formed by bending such as steel sheet, strip or plate, which channel member is open to one side and presents an out-turned flange, lip or edge at least along one edge of the opening, preferably a respective flange, lip or edge to opposite edges, the open channel being adapted to receive material retaining means which can be secured relative to the member to retain said sheet material trapped between the structural member and the material retaining means.

Preferably the material retaining means comprises one or more retaining members (preferably elongate) which are adapted to be received, wholly or in part, in the channel such that in use the sheet material to be retained is deflected to be contacted by and trapped between adjacent surfaces of the channel member and retaining member.

The retaining member may take different forms depending on the nature of the sheet material to be secured. For relatively thick materials such as high density polythene - say of the order of 1 mm thick (which is often used in perforate form as a wind break in horticultural applications), the retaining member may be top hat shaped in cross-section, affording a flange part presenting itself to the flange, lip or edge part of the .channel member, and having a protruding part or insert member dimensioned to be received in the open side or mouth of the channel member. In the preferred embodiment opposite flange parts are provided.It will be understood that the protruding part fits with clearance sufficient to accommodate the sheet material which on securing of the retention member in position, conveniently by a nut and bolt passing through aligned bores conveniently in the protruding part and a base of the channel member, undergoes deflection with resultant trapping of the sheet material usually between the flange parts aided by the deflection around respective edges of the parts.

Such a retention member can be used for fixing other types of sheet or reeled material of which wire netting is one envisaged material.

Another embodiment of retention member is specifically intended for securing more flexible sheet material, usually more easily damaged as a consequence, of which relatively thin polythene sheeting is typical, such as that used for covering polyhouses. In that embodiment, the protruding part or insert member takes precedence over the flange part of the aforementioned embodiment, indeed the flange part may be dispensed with entirely so that the retaining member be properly termed an insert member which is received wholly within the channel and serving to draw sheet material to be retained into the channel by a substantial amount, usually with an inner end face of the insert member coming to rest substantially adjacent to the bottom of the channel either closely spaced or in contact therewith.

In a preferred embodiment, the sheet (membrane) is drawn over a flange part of the member, and it is preferred to provide a shielding part over that flange part either as a separate member or a flange part of the retaining member, which shields the effect of sunlight on the membrane where it is in contact with the flange where high temperatures could otherwise give rise to membrane deterioration.

Holes drilled in the base of the channel at intervals can usefully serve to receive headed screws for cooperating engagement with the insert member to secure same in position. In relation to securing such thin flexible membranes great care has to be exercised to avoid damage to the membrane by nipping at points or lines of contact between the channel member and retaining member. Metal to metal contact has been found unsympathetic in such applications, indeed positively harmful, but the use of metal for one part such as steel, and a softer material for the other which exhibits some compliance, has been found to alleviate any problems. The material we have found most suitable for the retaining member is wood.

According to one embodiment of this invention then it is important that the member for retaining the sheet material and the retaining member are different materials, at least one of which exhibits some degree of springiness, compression or resilience.

We find that mild steel provides a particularly economical construction for said member, especially when formed by pressing into an open channel section with the edges of the channel formed with out turned flanges with radiused corners leading into the channel.

More particularly, at least one of those edges is turned back on itself or at least partially so to form a radiused edge. In one embodiment, the frame member has two elongate channel members disposed side by side defining in effect two troughs separated by a crest as viewed in the direction of insertion of the insert members. We prefer the steel to be coated with corrosion resistant material for environmental protection, such as galvanising or a plastics/resin coating. We prefer the channel to have side walls which converge, albeit only slightly, toward their connecting base, and for the thickness of the metal to be such as to impart structural strength to the frame to withstand any tension forces applied to it by stressing of the skin being retained, and yet to exhibit a limited degree of resilience on introduction of the insert members.

According to said one embodiment which is particularly suited to retaining relatively thin membrane materials we find that an insert member in the form of an elongate batten of wood works particularly well as it exhibits the desired degree of springiness and is particularly economical. Certain plastics having similar properties provide an alternative to wood. We prefer the wood to be dimensioned slightly larger than the width of the channel at its base, by upto approximately 2 mm, so that when pushed into the open channel the wood tries to force apart the sides of the channel and is itself subject to compression as a result of the forces exerted on it by the frame.

It will be understood that for the purpose of retaining the membrane it is disposed between the insert member and the channel so that on insertion of the insert member the membrane is drawn into the channel. The membrane is trapped where the corners of the insert member abut the channel sides substantially adjacent the base. The tapered configuration of the channel enables any thickness of membrane to be fixed with the same parts.

A further advantage of the system is that the kinder nature of the materials used enables tension to be applied in the fixing process without damage to the membrane. More particularly, in place of the small depth groove of the prior art, the channel of the frame member according to the invention is relatively deep, actually of the order 5 to 10 times the depth of the prior art groove and preferably the order of 38 mm deep. The effect of this is to be able to draw a length of membrane approximately equivalent to the depth of the channel into the channel on insertion of the insert member. This has to effect of drawing the membrane tight.

Once pushed home the insert member will remain in place, although repeated wind stressing and relaxing of the skin can give rise to creep so it is preferred to secure the insert in place either by such as screws or other fixing means passing through holes in the base and engaging into the insert member, or as an alternative by a snap fitting arrangement such as by mutually cooperating shoulders and lugs of the insert member and channel sides, say with a narrower mouth to the channel, or by a clip pushed home from the open side of the channel after fitting of the insert.

bne application of the membrane retention system is in relation to securing the membrane on polyhouses.

Having arrived at a membrane retention system which possesses inherent strength as well as a secure fixing for the membrane, it is possible to use that system in forming structural parts such as skinned frames made up of the members formed into a framework or even as spaced posts set into the ground between which sheet material can be retained. Use of the elements of the present invention is that context has the advantage of providing for tensioning of the sheet material by virtue of it being drawn or deflected into the member by the retaining means.

Accordingly, another aspect of the invention provides a skinned structure comprising a framework made up of at least one frame member defining an elongate channel open to one side, and one or more retaining members, preferably of different material to the frame member, and adapted to fit into the channel to retain there between a membrane located at an opposite part of the frame and thereby secure under tension said membrane across the frame.

More particularly, at least two of the sides are comprised of said frame member and retention of the membrane is by respective insert members in said frame members. In fact complete rectangular frame works can be built up using the frame members and insert members for retaining the four sides of the membrane stretched across the frame.

The various aspects of the present invention will now be described further by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a frame member and insert member; Figure 2 is an end view of the frame member and insert member of Figure 1 prior to insertion of the insert member; Figure 3 is an end view of the frame member with the insert member in position retaining the membrane; Figure 4 is a front view of a frame work built up of frame members and showing insertion members for holding a membrane stretched tight across the framework; Figure 5 is an end view of a polyhouse showing typical locations for the frame member of the present invention for holding the skin in place; Figure 6 is an end view of an alternative frame member; Figure 7 is an end view of a yet further embodiment of frame member; ; Figure 8 is a sectional view of a second embodiment for retaining less flexible sheet material; Figure 9 is a perspective view showing applications of the fixing system to fencing; and Figure 10 shows a modified insert member of Figure 3 having a head part for shielding the membrane material.

Referring firstly to Figures 1, 2 and 3 there is shown an elongate frame member 1 made of sheet metal such as steel and folded to define a channel 5 open to one side as at 7 and having side walls 9, 11 and a connecting base 13. Respective flanges 15, 17 are formed to the open side of the channel and connected by way of radius 19. The uppermost flange 15 is turned back on itself to form a radiused edge 21. As an alternative that radiused edge may be provided by a cover strip, say of plastics material fitted onto the edge. One or both of the flanges 15, 17 may be provided with such radiused edges.

The section of the channel is preferably arranged to converge towards the base by a small amount. The depth of the channel is preferably of the order of 30 to 38 mm in the direction of arrow x and the dimension of the base in the direction of arrow y is about 25 mm.

The width of the opening to the channel is preferably about 28 mm and with a maximum of'about 31 mm providing an equal taper to each side.

The preferred insert member 3 comprises an elongate batten of wood dimensioned to be received in the channel, actually preferred to be approximately 2 mm larger than the width of the base so as to force apart the sides of the channel on insertion in the direction of the arrow A. The batten is generally square or rectangular usually with finished sides. The membrane is shown at 23.

Referring now to Figure 3 the insert member has been pushed into the channel and has drawn in the membrane 23 trapping it at the corners 25. This drawing-in stretches the membrane material over the framework to which it is being applied by up to the depth x of the channel. A screw 27 is shown passing through a hole in the base and threaded into the wood to hold the insert member in place.

Referring now to Figure 5 there is shown end view of a typical polyhouse of multi-span type showing side by side hooped frames 29, also with end opening 31. The end opening is bounded by frame members 33, 35 and 37 constructed as per the frame member 1 of Figures 1 to 3 for receiving membrane which is pulled round the end hoop of the polyhouse and fixed by insertion of insert members in the direction shown by the arrows. With regard to positioning of longitudinal runs of the frame members for a multi-span house, one frame would be positioned adjacent to the gutter as at B and another to the opposite side of the house as at either C or D depending on the extent to which the membrane is to extend down the sides of the house. For a single house the gutter frame B would be replaced by one to the opposite side of the house corresponding in height to C or D or otherwise as required.The frame member B may be secured to the gutter 41 which itself may be a pressed steel construction or it is feasible for it to be formed integrally with the gutter and for the other side of the gutter to incorporate another frame B'.

It is frequently required for the roof part of the house to be skinned with such as translucent plastics sheeting and for the sides or at least part of the sides to be fitted with a different material such as one which allows ventilation say a netting and accordingly a further proposal of the invention is to have the frame member formed with two channels disposed side by side as illustrated at 43 and 45 in Figure 6.

Such a construction enables the membrane for the roof part to be pulled down and secured in the channel member 43 and for a different side membrane to be secured as at 45. The side membrane can then be removed and repositioned without disturbing the upper membrane or vice versa. The frame member is provided with radiused edges to both its ends to protect the membrane from chaffing. The alternative would be to fit two separate frame members.

Referring now to Figure 4 here we show how a skinned structure can be built up using elongate frame members similar to that illustrated in Figures 1 to 3.

In the illustration four frame members 50 are shown mitred at their ends and secured together, conveniently by welding or by some other convenient fixing clip embracing the ends and using screws or inherent resilience, so forming a structural framework over which is applied a membrane of sheet material. That membrane is secured in place across the frame by first fixing one insert member 52 into the open channel of the frame say at 50a to retain one side of the membrane and then inserting a further insert member 54 into the opposite channel 50b. Where top and bottom membrane fixing is also required then additional insert members illustrated as 56, 58 are employed to retain the top and bottom of the membrane.It will be understood that it is not essential for all the sides to be formed of frame members such as that described and to have membrane retention by means of the afore described insert member although at least one such fixing system is used in order to achieve stretching of the skin across the framework.

Referring now to Figure 7 there is shown a modified cross-section of the frame member 100 whose mouth 107 provides a narrow inlet to define shoulders 109 which serve to retain an insert member once pushed past the shoulders 109 this avoids the need for screw means for securing the insert member in place as it is held by the shoulders 109.

Figure 10 is a view similar to Figure 3 showing a modified insert member 3' having flange parts 103 extending beyond the flanges 15, 17. These serve to shield the membrane 23 where it is in contact with the flanges and so avoids excessive temperature build up in this area. The flange parts 103 are shown as integral with the insert member, which is convenient, but may be separate and secured thereto, in the manner of a capping.

Figure 8 is a view similar to Figure 3 but for the case of a less flexible membrane such as high density polythene sheeting. The member 1 is as per Figures 1, 2 and 3 or as modified in the manner of Figure 6, but the retaining member 3" is modified and comprises a generally elongate member which is top hat shaped in section, and conveniently formed as a pressing from steel strip having flange parts 111 and a protruding part 113 dimensioned to be received with clearance in the open channel of member 1. The protrusion is relatively shallow compared with the depth of the member 1 as the material 23' is not required to be drawn into the channel by any great extent, just to be deflected sufficiently to result in trapping of the sheet material between flanges 15, 17 and 111, the enforced bends being sufficient to resist pulling out in the direction of arrow X.It will be understood that the depth of the channel member 1 could be reduced for this embodiment, but requirements to accommodate insert member 3 in alternative embodiments suggests utilisation of the same member to minimise stocking requirements. A nut and bolt 2" so used to secure the retaining member to the member 1.

Referring now to Figure 9, here there is shown diagrammatically how the invention can be applied to the construction of fencing. The member 203 equivalent to member 3 of Figure 1 is mounted upright, actually shown bedded into the ground as a post, but could be secured to an existing. post. Fencing material 223 as a roll of sheet material is positioned over the posts, and the retaining member such as 3" secured in place so holding the sheet material in position, also serving to draw the material into the open channel to achieve tensioning of the material between adjacent posts.

Claims (26)

1. A member for retaining sheet material which may be perforate or imperforate and which exhibits at least some degree of deflection/flexibility, the member comprising an elongate channel member which channel member is open to one side and presents an out-turned flange, lip or edge at least along one edge of the opening, the open channel being adapted to receive material retaining means which can be secured relative to the member to retain said sheet material trapped between the structural member and the material retaining means.

2. A member as claimed in claim 1, wherein the channel member is of sufficient depth and rigidity to be self supportive.

3. A member as claimed in claim 1 or 2, wherein the channel member is formed by bending.

4. A member as claimed in claim 1, 2 or 3 wherein the channel member further presents a respective flange, lip or edge to opposite edges.

5. A member as claimed in any one of claims 1 to 4, wherein the channel member comprises an open channel section with edges of the channel formed with out-turned flanges with radiused corners leading into the channel.

6. A member as claimed in claim 5, wherein at least one of those edges is turned back on itself or at least partially so to form a radiused edge.

7. A member as claimed in any one of claims 1 to 6 wherein the channel member has two elongate channel members disposed side by side defining in effect two troughs separated by a crest as viewed in the direction of insertion of the insert members.

8. A member as claimed in any one of claims 1 to 7, wherein the channel has side walls which converge toward their connecting base, and is of such thickness of metal as to impart structural strength to withstand any tension forces applied to it by stressing of the skin being retained, and ye to exhibit a limited degree of resilience on introduction of the insert members.

9. A member as claimed in any one of claims 1 to 8, wherein the base of the channel is provided with holes at intervals to receive headed screws for cooperating engagement with the insert member to secure same in position.

10. A member as claimed in any one of claims 1 to 9, wherein the channel member is of mild steel.

11. A system for retaining sheet material comprising a channel member as claimed in any one of claims 1 to 10 and a retaining member insertable in said channel trapping sheet material therebetween.

12. A system as claimed in claim 11, wherein the retaining member is elongate.

13. A system as claimed in claim 11 or 12, wherein the retaining member is top hat shaped in cross-section, affording a flange part presenting itself to the flange, lip or edge of the channel member, and having a protruding part or insert member dimesioned to be received in the open side or mouth of the channel member.

14. A system as claimed in claim 11, 12 or 13, wherein the retaining member comprises an insert member which is receivable wholly within the channel and serves to drax sheet material to be retained into the channel by a substantial amount.

15. A system as claimed in claim 14, wherein an inner end face of the insert member when received in the channel comes to rest substantially adjacent to the batter of the channel either closely spaced or in contact therewith.

16. A system as claimed in any one of claims 11 to 15, wherein the retaining member has a shielding par over the flange part of the channel either as a separate member or as a flangs part of the retaining member.

17. A system as claimed in any one of claims 11 to 16, wherein the member for retaining the sheet material and teh retaining member are different materials, at least one of which exhibits some degree of springiness, compression or resilience.

18. A system as claimed in any one of claims 11 to 17, wherein the retaining member is of wood.

19. A system as claimed in any one of claims 11 to 18, wherein the insert member is in the form of an elongate batten of wood.

20. A system as claimed in claim 19, wherein the wood is dimensioned slightly larger than the width of the channel at its base by upto approximately 2mm.

21. A skinned structure comprising a framework made up of at least one frame member defining an elongate channel open to one side, and one or more retaining members and adapted td fit into the channel to retain therebetween a membrane located at an opposite part of the frame and thereby secure under tension said membrane across the frame.

22. A structure as claimed in claim 21, wherein at least two of the sides are comprised of said frame member and retention of the membrane is by respective insert members in said frame members.

23. A structure as claimed in claim 21 or 22, wherein the frame members and retaining members are of different materials.

24. A channel member substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.

25. A system for retaining sheet material substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.

26. A skinned structure substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.