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Publication numberUS3844080 A
Publication typeGrant
Publication dateOct 29, 1974
Filing dateJan 26, 1973
Priority dateSep 8, 1971
Publication numberUS 3844080 A, US 3844080A, US-A-3844080, US3844080 A, US3844080A
InventorsJ Brock, A Gillan, A Marden, A Pancewicz
Original AssigneeIci Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Suspended ceiling
US 3844080 A
Abstract
A suspended ceiling comprises a track secured to a basic building structure around the periphery of the ceiling, and a flexible membrane attached at its edges to the track by a multiplicity of individual suspension members extending outwards from spaced-apart points along said edges and engaging the track so as to be movable therealong, the membrane being thereby stretched across the area defined by the track. The membrane may be subdivided into a plurality of discrete panels preferably suspended from intermediate track located between adjacent panels. Channel sectioned trunking can provide a versatile track.
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Description  (OCR text may contain errors)

roclr et all.

[ 1 susrnnnnn CEllLlNG [75] Inventors: James McFarlane Brock,

-. Knebworth; Anthony David Gillan,

Hoddesdon; Adrian Mai-den, Welwyn Garden City; Arthur Christopher Pancewicz, Connington near Peterborough, all of England [73] Assignee: Imperial Chemical industries Limited, London, England [22] Filed: Jan. 26, 1973 [21] Appl. No.: 326,958

Related US. Application Data [63] Continuation-in-part of Ser. No. 178,888, Sept. 8,

1971, abandoned.

[30] Foreign Application Priority Data Feb. 2, 1972 Great Britain 4838/72 Oct. 13, 1972 Great Britain 47292/72 [52] US. Cl 52/222, 52/484, 52/509, 52/511 [51] int. Cl E040 5/52 [58] Field of Search 52/63, 273, 511, 509, 231, 52/222, 23, 291, 484; 160/327, 328, 329, 404; 272/65 3,355,745 12/1967 Jannuzzi; 52/63 X 3,375,861 4/1968 Merlow 3,386,220 6/1968 Staats 3,405,489 10/1968 Frisk 52/222 3,564,784 2/1971 Mollinger 52/222 X 3,583,115 6/1971 Colmenares 52/484 X 3,683,427 8/1972 Burkholz 52/222 X FOREIGN PATENTS OR APPLICATIONS 1,073,182 6/1967 Great Britain 52/309 193,877 2/1932 Switzerland. 160/327 638,735 3/1962 Canada 272/65 1 256,293 2/1964 Australia 272/65 643,419 9/1950 Great Britain 52/63 323,189 4/1970 Sweden 52/222 1,317,152 3/1962 France 52/484 80,633 4/1963 France 52/484 Primary Examiner-John E. Murtagh Assistant Examiner-Leslie A. Brown Attorney, Agent, or FirmCushman, Darby & Cushman [5 7] ABSTRACT A suspended ceiling comprises a track secured to a basic building structure around the periphery of the ceiling, and a flexible membrane attached at its edges to the track by a multiplicity of individual suspension members extending outwards from spaced-apart points along said edges and engaging the track so as to be movable therealong, the membrane being thereby stretched across the area defined by the track. The membrane may be subdivided into a plurality of discrete panels preferably suspended from intermediate track located between adjacent panels. Channel sectioned trunking can provide a versatile track.

14 Claims, 11 Drawing Figures PATENTEDOCI29I9?4 Y 31844086 manor 6 FIG 7 1 SUSPENDED CEllLlNG This applicationis a continuation-in-part of our earlier application Ser. No. 178,888 filed Sept. 9, 1971 and now abandoned.

The present invention relates to suspended ceilings in which a flexible membrane is stretched under a soffit to improve acoustic properties, to improve thermal insulation or as a decorative finish. Suspended ceilings are generally constructed either as a series of rigid plates supported by a grid, or as a flexible membrane attached at its edges to the basic building structure and maintained under considerable tension to reduce the sag to a tolerable level. It is the latter class of suspended ceilings to which the present invention relates.

Previously, typical ceilings of this class have been formed from a plastics foil, such as polyvinyl chloride, and secured to the building structure by means of rigid timber battens or V-section plastic strip secured to the edges of the membrane, the battens being secured to the basic building structure, and the V-section strip cooperating with a second strip secured to the basic building structure and having a projecting fillet for the engaging of V-section strip, respectively. The battens or strip could either be secured to the membrane under ideal factory conditions whence they made folding of a membrane for transportation difficult, or they could be secured to the membrane on site under often difficult and unsuitable conditions. Where rigid battens secured to the membrane prevented the edges from stretching, and where rigid extrusions had to follow irregular walls, e.g., around chimney breasts or bay windows, there was a tendency for wrinkles or creases to occur indicating uneven stresses in the membrane; and to overcome these problems, it had been suggested that the operators erect the ceilings in a heated atmosphere. Furthermore, in order to obtain the required stretch with such systems, the stretching forces required were generally sufficiently high to require the transportation of hydraulic equipment to and from each erection site.

According to the present invention, we provide a suspended ceiling comprising a track secured to a basic building structure around the periphery of the ceiling,

. and a flexible membrane attached at its edges to the track by a multiplicity of individual suspension members extending outwards from spaced-apart points along said edges and engaging the track so as to be movable therealong, the membrane being maintained thereby in a stretched condition across the area defined by the track.

The track is preferably formed from a plurality of tubular members arranged end-to-end around the periphery of the ceiling. We find that one of the most time consuming phases in the erection of the ceilings is in the securing of the track to the basic structure. We therefore prefer the track to have sufficient rigidity to allow its securing means to be spaced apart by conveniently large distances, e.g., 60-120 cm. Conduit tub ing, suitably between and mm outside diameter, is particularly convenient because of its availability. [t is further preferred to interconnect the ends of adjacent tubular members by short rigid members inserted into the end of the tubes. In this manner, alignment of the two adjacent ends may be maintained without the need for securing each end separately to the basic building structure, or in the case of a corner, the ends of the two members may be maintained at their predetermined angle.

Any convenient means may be used for securing the track to the basic structure but we prefer to use a plurality of hooks shaped to receive the track, said hooks having a threaded shank for attachment to the basic structure.

The suspension members preferably have a hookshaped end for-engaging the track. Thus, for example, where the track is conduit tubing, the end of the member is hooked around the conduit so as to engage the surface of the conduit remote from the membrane when the ceiling is assembled. We further prefer the suspension members to be hook-shaped at their ends remote from the track so that they may be simply attached to the membrane by passing the hooked end through spaced-apart holes or into a pocket therefor in the membrane. ln assembling our preferred ceiling, we find that it is more convenient to provide the hooked ends extending in opposite directions, and so our preferred suspension members are of a generally S-shaped configuration, and these may readily be formed very cheaply from spring steel wire, conveniently of about 2 mm diameter.

The spaced-apart points of the membrane from which it is suspended enable the edges of the membrane to stretch along with the remainder of the membrane during assembly of the ceiling and so avoid the wrinkles associated with uneven stresses. The membranes generally require some form of reinforcement, however, to reduce tearing and bowing of the edges to an acceptable level. Hence when any rigid inextensible reinforcing members, such as, eyelets, small rigid plates, battens or the like, are secured to part of any one edge of the membrane in such a manner as to prevent that part of the edge from stretching, the total length of that part of the edge which is pre ented from stretching by the reinforcing members should be less than 20 percent, and preferably less than 10 percent, of the length of that edge. A preferred manner of spreading the load, however, is to provide the edges of the membrane with rigid or semi-rigid members which spread the load over their entire length, but which allow the membrane to slide along them to accommodate the stretch. 7

Hence, in a preferred ceiling, the membrane has along each of its edges a hem providing a pocket within which is slidably located one or more rods preferably arranged substantially end-to-end along the edge, the rods being positioned with respect to the suspension members such that the tensile forces stretching the membrane are applied by the suspension members to the rods, said forces being thereby spread along the edge of the membrane. Each rod is preferably at least 30 cm in length, so as to provide a good spread of the load, but the upper limit to the length depends both on the ease of handling during assembly, and in some circumstances on therequired shape of the membrane. We have found it convenient in domestic rooms to use lengths of rod within the range 30 to cm particularly about 60 cm, but longer lengths may be used to advantage for long corridors and the like, particularly where only low membrane stretch is required. The pocket conveniently has openins at like distances to enable the rods to be inserted. The hem may be sewn or welded to the membrane as appropriate.

It is intended that the manner in which the suspension members transmit the load to the rod is such that it will not prevent the membrane sliding over the rods as it is stretched. This may be conveniently achieved when using suspension members which are hookshaped at their ends remote from the track, by arranging for those ends during assembly to penetrate the membrane on the sides of the rods remote from the track so that they become hooked around the rods. The position of the hooks with respect to the membrane is thus determined by the location of the hook within the hole in the membrane, and so the hooks move with the membrane as the latter stretches, permitting even tension throughout the membrane. Assistance in sliding the hooks along the track e.g. by tapping them into place, may generally be helpfully provided as required.

The membrane may be formed from a thermoplastic foil, such as polyvinyl chloride foil, but such foils tend to require considerable reinforcement and high stretch. We prefer to use a melded fabric. Melded fabrics are non-woven materials containing composite filaments, which are strengthened and stabilised by potentially adhesive characteristics of one of the components of the composite filaments. The adhesive properties may be activated for example by chemical reaction, or by the application of heat to a web of the filaments, generally in association with applied pressure. We particularly prefer a melded fabric comprising composite filaments having a core of polypropylene sheathed with a layer of polycaprolactam, whose adhesive properties may be activated by steam heating. The fabric may be formed by passing a web of the filaments through a steam chest from which it emerges between rollers. Suitable filaments for forming the (non-woven) fabrics are those sold under the name Cambrelle. The non-woven fabrics may also contain suitable single component filaments such as polypropylene filaments, in addition to the composite materials. Non-woven fabrics made from composite materials and methods of making them are described in United Kingdom Pat. specification No. l 073 182, and we find that in comparison with polyvinyl chloride foils, such fabrics provide several advantages. For example they are generally tougher and stiffer, and give very little sag even with a very low degree of stretch, a stretch of 0.5 to 5 percent generally being suitable. To obtain an even stretch of 0.5 percent, however, requires very accurate cutting of the membrane and assembly, since this figure becomes drastically reduced by even small errors in membrane size. Thus although a 0.5 percent stretch is sufficient, in practice we generally prefer to aim for a stretch of about 2 percent.

Where combustible fibres are used for making the non-woven fabrics, we prefer to coat the fabric with a fire retardant coating, and where the fabric is so protected, we find that the effect of a fire below the ceiling is less dramatic than the effect of a fire below a polyvinyl chloride foil ceiling. The non-woven fabric does not run before the fire as much as does the foil, partly on account of the increased stiffness and partly due to the lower stretch employed. ln particular, whereas a polyvinyl chloride foil tends very quickly to draw away from above the flames and to droop down over the walls and hence over fire exits in the walls, the coated melded fabric merely chars and becomes very weak and brittle and does not present that fire hazard.

Because heaters and hydraulic stretching equipment are not required when using our preferred fabrics, ceiling erection is within the capabilities of most do-ityourself" enthusiasts and semi-skilled labour, although the difficulties in handling large areas of material make it easier to first prepare the membrane for each specific job before dispatch from the factory. Since conduit track is readily available, the ceiling may conveniently be dispatched in the form of a kit comprising a membrane and a multiplicity of suspension hooks, the membrane being cut to size and its edges adapted to receive the hooks.

Because of the difficulties involved in forming and erecting very large areas of membrane material, for many applications in which a large area of ceiling is required, we find it more convenient to use a plurality of discrete panels of the same flexible material. We also find that smaller areas may be more versatile in some applications by permitting reassembly and adjustment of part of a larger area without affecting the remainder. We now find that we can form a celing from a plurality of discrete panels by employing an intermediate track between adjacent panels, the panels being attached to the intermediate track using a plurality of individual suspension members in a manner substantially the same as that referred to above for attaching the membrane to the track around its periphery: hereinafter referred to as the peripheral track when it is to be distinguished from the intermediate track.

The intermediate track may be supported by its own rigidity, but we usually prefer to provide additional support. For example it may be suspended from an overlying soffit, or it may be secured to or form part of a grid which is itself secured to the basic building structure. When the intermediate track is suspended from an overlying soffit, a flexible suspending means, e.g., wire, is preferred for most purposes so that the lower end may be displaced during assembly or subsequent partial disassembly due to the tension in the stretched fabric without permanent distortion or fatigue. However, where it is important to avoid such movement, e.g., where rigid service ducts and the like are also supported by the same suspending means, the ceiling may be provided with one or more bracing straps traversing the ceiling from wall to wall in a direction perpendicular to that of the intermediate track, the bracing straps being attached to each suspending means or track in turn.

We generally prefer the intermediate track to have the same operative features as the peripheral track, any unidirectional feature being duplicated in the intermediate track as required by the presence of membrane panels on both sides of the track. In this way the same kind of suspension members may be used in conjunction with both tracks. Simple cylindrical tubing, e.g., conduit, is often particularly suitable being of low cost and generally readily available. More versatile ceilings may be obtained however by using selected sections for the intermediate track. A particularly versatile intermediate track is one having an inverted channel section comprising a base with two downwardlydirected sides each having an inwardly directed lip extending along its lower edge, the panels being attached to the intermediate track by a multiplicity of individual suspension members spaced apart along an edge of each panel and hooked around the adjacent lip of the track.

The shape of the lip is unimportant provided that the shape of the suspension hooks is compatible with it so that they do not fall off, e.g., when the tension of the membrane is reduced, and the lips may therefore be shaped to suit particular requirements. Thus the lip may be a flat flange coplanar with or parallel to the membrane, or it may be at any other angle between the two vertical extremes of the 180 quadrant directed away from the membrane. It will be realised, however, that at the extreme angles where the lip is a flange approaching the vertical, it becomes increasingly difficult for the hooks to engage the lip sufficiently securely for practical purposes. A section which is particularly useful when it is necessary to tie together the two sides to prevent the channel opening up under load, is one in which the lip has a longitudinally extending upstand parallel to the side of the channel so as to provide a recess therebetween, so that at intervals along the track a bridging member may be located in the two recesses to securely engage both sides of the channel. For simple shapes of track, the lip may be formed, for example, by the sides of a channel being rolled or folded inwards one or more times.

Because of its ready availability and developed versatility, we prefer to form the track from trunking such as that presently available for forming the grid in the type of suspending ceilings wherein individual rigid panels are supported on a grid. In this manner, the versatility of the grid system can be bestowed on our stretched membrane kind of ceiling while still retaining many of the advantages which the stretched membranes have over the rigid tiles, particularly when the panels are in the form of parallel strips extending the entire length or width of the total area.

On aesthetic considerations, the open side of the trunking channel may be covered by some form of cover strip, thereby concealing all the services such as electric cables. compressed air lines and the like which may be carried along the trunking. Moreover, we prefer to use a cover strip which extends outwardly sufficiently to hide the edge detail of the membrane suspension, and hence avoid having to provide a separate cover strip for that purpose.

The suspension hooks described above for use with conduit are generally S-shaped. Similar hooks may be used with trunking, but we find it more convenient with most forms of such flanged track, to turn the two ends of the member in the same direction so as to produce an elongated C -shaped hook. This shape is a generalisation, however, and the precise shape preferred for any particular shape of track flange may be a modification of this generalised elongated C-shape.

By forming the ceiling from discrete panels, it enables the erector to stock only a single standard width of membrane fabric, e.g., 2 m wide, which may then be cut to the required length either in the factory or on the site. Moreover, when using trunking or similarly suitable track, lighting fittings and the like may be very simply secured to the trunking and powered through electrical wiring carried along the trunking, the erector being free to secure the fittings and wiring either before or after the membrane panels have been fitted as may be most convenient. To the user of such ceilings, the provision of discrete panels enables ready access to be made to a soffit above the membrane, while disturbing only a small part of the ceiling. Moreover. by using trunking, the user is enabled to reach the electrical wiring or other power lines carried in the trunking, without any disturbance of the ceiling membrane. This access may be necessary, for example, for maintenance, or for alterations such as the provision of further lighting, or rearrangement of the lighting, telephones, air fans, power tools and other apparatus requiring electrical, compressed air or other power supply lines. Where larger rooms are subdivided into smaller rooms by demountable partitions, the use of standard commercial trunking enables these partitions to be secured at their upper edges in known manner, and provides the user with a versatile system which can be varied considerably to suit his requirements.

Although the use of an intermediate track is preferred because of the simplicity of erection and versatility of particular tracks, the adjacent panels may alternatively be directly interconnected by a multiplicity of individual suspension members, e.g., wire hooks, at least some of which are suspended directly from the soffit. The suspended books may be attached to a separate suspending means, or may form part of an integral suspension unit hanging from the soffit and engaging one panel on each side. The individual hooks may be linked to form a single unit, but in that case the means linking the hooks together should be free to stretch evenly throughout its length to the same extent as the material used for forming the panels.

To illustrate the invention, specific embodiments thereof will now be described by way of example, the embodiments being illustrated in the accompanying drawings in which:

FIG. I is an isometric view of the underside of a small area at the edge of a ceiling showing the suspension means,

FIG. 2 is a section through part of the suspended membrane and one of the suspension members, viewed in a direction parallel to an edge, and showing edge reinforcement which is a modification of that shown in FIG. 1,

FIG. 3 is an isometric view of the stretching tool employed in the assembly of the construction,

FIG. 4 and 5 illustrate alternative shapes for the suspension hooks,

FIG. 6 is a section through the edge of a membrane showing also in section an alternative bracket for securing conduit to the basic building structure, and means for securing a coving for covering and hiding the suspension means,

FIG. 7 is a section through the edge of a ceiling similar to that shown in FIG. 6 but employing a number of alternative features,

FIG. 8 is a section through part of a multiple panel ceiling, in a plane perpendicular to the lines of join between the panels. The span between adjacent joins has been foreshortened, and details not in the immediate vicinity of the plane of section have been omitted for clarity,

FIG. 9 is a section through an alternative form of intermediate track shown in use, and

FIGS. l0 and 11 are sections through alternative peripheral tracks particularly suited for use in ceilings employing the intermediate track of FIG. 9.

The suspended ceiling illustrated in FIG. 1 is formed from a membrane comprising a non-woven fabric 1, to the edge of which is sewn a 50 mm wide strip of hessian 2. The non-woven fabric is made from a fibrous web comprising about 50 percent polypropylene monofilament and 50 percent composite filament having a core of polypropylene and a sheath of polycaprolactam, the fibres having been bonded by softening the polycaprolactam with steam and then applying pressure to the web by passing it between rollers. 13 mm diameter brass eyelets 3 are let into the hessian at 150 mm intervals, the stitches 4 and the outer edges of the eyelets 3 being located about 6 mm from the opposite edges of the hessian strip 2. The membrane has a fire-retardant coating which also renders the fabric substantially nonpourous to air, and which was applied to the fabric before the ceiling was assembled. The coating comprises 40 parts by weight of a butadiene/styrene latex ("Revinex 9210"), 3 parts by weight of antimony oxide, 8 parts by weight of titanium dioxide and 40 parts by weight of a fire-retardant composition, comprising 59 percent of ammonium bromide and 41 percent of a solution of phenol-terminated polyethylene oxide in ammonia.

The track is formed from 19 mm external diameter conduit secured to a wall by standard conduit clips leaving a gap of about 3 mm to 6 mm between the conduit and the wall. The suspension members comprise wire S-shaped hooks 6 which pass through the eyelets 3 in the hessian 2 and are looped under and behind the conduit 5.

The ceiling was assembled and secured to a 366 cm square basic building structure by the following steps. The coated non-woven fabric was cut to a size of 348 cm square and sewn at its edges to the hessian strip 2, the eyelets 3 then being inserted. The conduit was then attached to the wall by means of the clips to form a continuous track at the height desired for the final ceiling. The smaller end of the hooks 6 were then inserted into the eyelets and those hooks along one side of the membrane were attached to the conduit by hooking their larger end around the conduit. The hooks along the other three sides were then also hooked around the conduit in turn, starting with the side adjacent that already attached, and finally drawing the remaining membrane edges and the conduit together, using a manually-operated tool as illustrated in FIG. 3 where required during application of the stretching forces. The suspension means and hessian strip occupied about 64 mm at each edge, so that the linear extension which was applied to the membrane was about 51 mm, giving a percentage stretch of about 1.5 percent.

The amount of extensible reinforcement required, if any, will depend on thenature of the material used for the membrane, but common to all materials is the necessity for the reinforcement to be such that the edges of the membrane may be allowed to stretch evenly with the remainder of the ceiling during assembly. For example, as illustrated in the drawings, we find that hessian strips, conveniently having a width of 20 to 50 mm, or the edges of the fabric folded over to provide two or more layers of material, are particularly suitable for reinforcing the edges of non-woven materials.

In FIG. 2, the edge of the non-woven fabric 21 is reinforced with a mm wide strip of hessian 22. A row of 13 mm diameter brass eyelets 23 are again provided along the edge of the membrane, but in contrast to that shown in FIG. 1, the eyelets penetrate both the hessian and the non-woven fabric and hold them together thus reinforcing the stitches 24. The membrane is again suspended from a conduit track 25 by wire hooks 26,

stretching of the membrane being assisted by use of the tool illustrated in FlG. 3.

The tool illustrated in FIG. 3 comprises a first lever 31 connected to a second lever 32 by a hinge 33. Both levers are formed from two plates held in a spaced apart configuration by spacers (not shown) such that the ends of both plates of the first lever 31 are located between the ends of the two plates of the second lever 32 at the hinge 33. The first lever is provided with a stop 34 formed from a dowel interconnecting the two plates. An operating member 35 is connected to the second lever 32 by a hinge 36, and passed between the two plates of the first lever 31 so as to engage the stop 34. The first lever 31 is provided with a squaresectioned transverse bar 37 extending outwardly for 25 cm on both sides of the lever. Slidably mounted on the bar 37 are two blocks 38, one each side of the lever 31 and each block 38 carries a projection 39 adapted to engage an eyelet of the membrane. Each of the plates of the second lever is provided at the free end with a hook 310 shaped to provide a firm location around the conduit, and at its hinged end the second lever is provided with a transverse load-spreading plate 311. The total length of each lever, excluding the hooks, is 30.5 cm.

For ease of handling, the operating member 35 may be extended by a separable portion 312 formed from a length of steel tubing into the end of which the member 35 may be inserted. The outer end of the extension tube has a padding transverse bar 313. The mechanical advantage of the tool increases as the projections 39 holding the edge of the membrane approach the track, the overall mechanical advantage being about 2. This is a value we found convenient for use when providing an extension of about 2 percent in a non-woven fabric. When the tool is required to be opened to a greater extent, either to apply a large degree of extension or to stretch a long length of fabric, we prefer that the projections 39 by angled towards the hooks 310 to stop the eyelets from sliding off them during the stretching process. Similarly, where extra movement is required or large forces encountered, the dimensions of the tool may require suitable adjustment.

When erecting ceilings which have a hem along the edge and rods inserted in the pockets so produced, no eyelets are provided for location on the projections. Under those conditions we prefer to replace the illustrated projections by projections having sharpened ends so as to pierce the fabric, the projections being inclined towards the hooks 310 in order to assist further penetration of the membrane as the stretching forces are applied, thereby holding the membrane more firmly. The membrane is preferably pierced immediately behind the rod within the pocket, so that the load may be spread along the edge by the rod.

1n assembling a wall or ceiling construction using the tool of FIG. 3, the membrane-engaging hooks 39 are inserted into eyelet holes in the edge of the membrane, and the conduit-engaging hooks 310 are located around the conduit. The spreader plate is placed against the wall of the building and the operator then leans against the padded transverse bar 313 to draw together the two sets of hooks, his hands being free to position the suspension hooks which have been previously inserted into the eyelets around the conduit.

The shape of the suspension hooks is not critical and may, for example, be generally S or C shaped, provided the ends have sufficient curvature to prevent slipping under tension. The shape which we find particularly convenient is illustrated in FIG. 4, the smaller squared end being located in the eyelet of the membrane. lf desired, the suspension members may be sprung, but complicated springing causes an increased expense which fo most purposes is unnecessary. However, a simply sprung hook is one having a Z configuration in the plane of the membrane with orthoganol hooks at either end, a spring of this kind being illustrated in F IG. 5.

Alternative forms of track and corresponding runners which may be suitable include, for example, track formed from slotted L-sectioned or channel members, or may be essentially T-sectioned having twin-wheeled or C-sectioned runners of the type generally used for certain rails.

As an alternative to the standard conduit clip, we have found a simple strap passed around the conduit and secured to the basic building structure by means of a single screw, to be cheap to produce and simple to install. A suitable strap is illustrated in FIG. 6, which shows the conduit 61 attached to a wall 62 by a metal strap 63 looped around the conduit 61 and secured to the wall 62 by a screw 64. The screw 64 passes through a hole 65 in each end of the strap, a washer 66 being provided to spread the load. The conduit is shown providing suspension means for a membrane 67 formed from a non-woven fabric, the edge of the membrane being reinforced by employing three layers of the nonwoven fabric fastened together by an adhesive and 13 mm diameter brass eyelets 68 located at cm intervals along the edge. The membrane 67 is connected to the conduit by books 69 looped through the eyelets 68.

To assemble the construction, the conduit 61 is first hung from the wall by the straps 63. The edge of the fabric is folded over and held in position by the adhesive. Where a suitable coating; e.g., a fire resistant polyurethane elastomeric coating, is applied to the fabric, this may conveniently be used as the adhesive. The eyelets 68 are then inserted through all three layers of the material, and hooks 69 fitted. These are then looped around the back of the conduit 61 using a stretching tool as required. The conduit is thereby pulled away from the wall until it is in the general position illustrated in FIG. 6.

It is often convenient to provide an adjustable bracket, particularly where the basic building structure is not perfectly in line. This may conveniently be achieved by using a strap which is suitably slotted to allow for adjustment, or by using a strap provided with alternative holes for receiving the screw. The conduit is then initially suspended using substantially the correct length of strap. Subsequent adjustment of the strap length is generally difficult to carry out on the assembled construction, but because of the ease with which the membrane may be detached and reattached to the conduit. any necessary corrections to the length of the straps may readily be made after unhooking the membrane at least in the region of the strap.

H6. 7 shows one edge of a suspended ceiling in which a membrane 71 is stretched between the walls 72 of a basic structure. The membrane 71 is a non-woven fabric of the kind described in connection with FIG. 1, but the edges of the membrane are turned over to form a hem 73 held by stitches 74 and thereby provide a pocket 75. Within the pocket are bright mild steel rods '76 of about 5 mm diameter and 60 cm long, arranged substantially end-to-end along the pocket, shorter lengths of rod being used where necessary to complete the full length of each membrane edge. Around the periphery of the ceiling is a track formed from standard l9 mm outside diameter conduit tubing 77 secured to the wall by hooked screws 78. The membrane is attached to the track by books 79 of the shape illustrated in FIG. 4, and the suspension assembly is hidden from sight by a coving 710, cm wide and approximately 1 mm thick, formed by extruding a resilient polyvinyl chloride. On the hidden surface of the covering is a ridge 711 having an upstand 712 which is located behind the ends of the suspension hooks 79. The edges of the coving press against both the membrane 71 and the wall 72 so that it becomes arched, and is retained in position by its resiliency.

The manner-in which the ceiling of FIG. 7 may be erected is illustrated by the following description of a trial erection carried out under site conditions. A rectangular room approximately 7 m X 6 m was provided with a suspended ceiling using the non-woven fabric described above. A roll of fabric was first provided with a fire retardant coating by being passed from a storage roll to a bath containing a fluid composition comprising 200 parts by weight of ammonium bromide solution (60 percent by weight of ammonium bromide), 24 parts by weight of titanium dioxide, 15 parts by weight of antimony dioxide, 120 parts by weight of a butadiene/styrene latex (Revinex 9,210) and sufficient of a thickening agent (Revertex A191") to provide the desired viscosity. This last quantity was found to vary between batches, but was always small, being of the order of only 3 parts by weight. The coated fabric was then passed upwards between infra-red heaters to dry the composition, and rewound onto a second roller, where it was available for use as required. The coated fabric was then unwound, marked, cut to the required size and provided with a 1.5 cm hem along all its edges, giving a membrane having dimensions of 580 cm X 680 cm. The prepared membrane was then folded and transported to the room for erection.

The walls of the room were drilled at intervals of about 60 cm, at a height of about 180 cm. In order to carry out the drilling operation at this height above the level of the operators head, the drill was held in a jig comprising two telescopic legs joined by crossmembers, by a base at their lower end and at their upper end by a holder for the drill. A water level was secured to the jig at approximately the eye level of the operator, and was set at the outset. The legs of the jig were adjusted to the desired height, and the holes drilled in turn, the leg length being checked against the water level so as to maintain a horizontal ceiling, independent of variations in floor level. The screwed books 78 were then screwed into the holes by holding each hook in a slotted chuck on the drill, still retained within its ig.

The track was assembled from conduit pre-cut into lengths of 60 cm, cm and cm, these lengths having been chosen for ease of transport and convenient assembly. Shorter lengths were cut on site and used as required to complete the length of track needed for each side of the room. The lengths of conduit were dropped into the supporting hooks, and adjacent ends joined by short solid members inserted therein.

The membrane was then unpacked, and the first edge hung from the track along one side of the room by a few prepositioning clips. These consisted of a spring clip suspended from a hook engaging the track. The membrane was then unrolled and suspended from the track as it progressively unrolled, until it was arranged approximately in position, but without edge reinforcement or tension.

Reinforcement of the edges was theneasily accomplished on the prepositioned membrane by cutting the hem at intervals and inserting the rods 76. The suspension hooks 79 were pushed through the fabric around the rods as'shown in HQ 7, and then hooked around the track, the prepositioning clips being discarded as they were progressively made redundant by the suspension hooks. As before, a stretching tool was used in the later stages to pull the membrane towards the track, the pull being relatively small as a stretch of only about 1.5 percent was used. Although such a low stretch was used, there appearedto be little or no sag. Finally, the coving 710 was clipped into place around the edges to hide the means of suspension. Throughout the entire procedure from drilling the walls to attaching the coving, the operator wore stilts such that his head was a little below ceiling level.

When using a membrane coating like that described above, which is corrosive in respect of the mild steel used for the rods, we prefer to use rods having a suitable protective coating. Polyethylene coatings are generally suitable.

The advantage of using the screwed hook for supporting the conduit in preferance to the straps 63 of FIG. 6 which provide equally good support, resides in its ease of assembly. Thus a geared down power drill having a slotted arbor,-or slotted holding means held in thechuck, provides a positive grip on the hook, even when the drill is held in a jig operating at ceiling level above the operators head. This avoids the difficulty of preventing a power driven screw-driver from destroying the screw head slots when incorrectly located in them.

For suspending the membrane from the track, the rigid hooks illustrated in F lGS. -2, 4 and 5 are very simple to use, and are therefore preferred. However, nonrigid suspension members such as flexible tapes, may alternatively be employed.

Coving of the section illustrated in FIG. 7 is convenient in that it may be rolled up for transportation to the site, where it is simply unrolled, cut to size and clipped in place. It is held particularly firmly by means of its enforced curvature, where the longitudinal edges are braced against the wall and membrane, counterbalanced by the tension in the ridge 711. The corners may be finished off by adhesive tape, moulded comer pieces, or like means. The double curvature of the corner join however, is not the simplest of joins to make neatly, and other shapes, such as a box section having straight sides parallel to the wall and membrane respectively, may be used as alternatives, although such shapes may be held less securely in place or may be more difficult to roll for transportation.

Alternative covings may be used, and any of the usual adhesively mounted covings formed for example from expanded polystyrene, may be employed. However, by securing the coving in a substantially permanent manner, the structure may be deprived of its feature of ease of removal and reassembly. We therefore prefer to use a coving which simply clips into place, or is otherwise removably secured. One method we have successfully employed is also illustrated in FIG. 6, in which a coving 610 is provided with wedges 611 spaced apart at intervals therealong, and which are a push fit between the conduit and the wall. These wedges may be formed from timber, in which case it is preferable to machine therein a slight depression to receive the conduit to prevent drop-out in the event of stretch or settling in the strap. Alternatively, the wedges may be formed from deformable material, which may be a resiliently deformable material such as rubber, or a more permanently deformable material such as expanded polystyrene or balsa wood. The covings may be formed of any suitable material which is sufficiently rigid to prevent unsightly sag, and may be formed, for example from paper or a thermoplastic foil. Lips 612 and 613 may be provided to increase the rigidity and ensure contact against the ceiling and wall by applying a slight pressure against them. The wedges may be attached to the coving by, for example, adhesives or staples.

With the present method of suspending the membrane, all work which involves the final shape of the membrane may be completed at the factory under conditions which are generally far more favourable than those usually found on the erection site. When the fabric has been cut to the required shape and provided with a hem or hessian strip, the shape of the unstretched membrane has been finally determined. The completed membrane may readily be folded for its transportation to the site, and in particular may be folded in the manner which renders it most accessible for erection having regard to the shape of the basic structure, without the constraints associated with rigid battens or damagcable semi-rigid edge strip. Moreover, once the fabric has been obtained, the ceiling may be assembled using readily available materials such as conduit, screw hooks, steel rods or hessian and eyelets for reinforcing the edges and steel wire for forming the suspension hooks. All materials and essential tools are readily transportable to the site, and no expensive hydraulic stretching equipment is necessary for out preferred embodiments.

One of the features of our preferred form of suspended ceiling in which a non-woven fabric is suspended from a track by simple hooks, is that the membrane may readily be removed and reassembled repeatedly, and as with new ceilings, this may be carried out without expensive equipment. This is particularly advantageous where the ceiling hides a cavity to which access may occasionally be required. The cavity may contain, for example, automatic or remotely controlled machinery requiring occasional attention for maintenance or repair, or water and electrical supplies where access for inspection or repair is advantageous.

Our preferred ceilings, that is those whose membranes are melded non-woven fabrics formed from composite fibres such as Cambrelle fibres, may be used to support directly thermal insulants and lightweight fittings such as diffusers, without further support. Similarly, lightweight radiant heating systems, such as those sold under the name Flexel, may be laid directly on the membrane, with insulation added above the heating elements to provide a particularly efficient location for the heater. Thus for example when a membrane which had been stretched by about 1.5 percent in each direction was covered by Flexel heating units,

l3 which in turn were covered with a 75 mm layer of glass fibre insulationwe found that the sag was of the order of 0.5 percent of the shortest span.

Acoustic absorbent may be supported in the soffit above the ceiling, or again where lightweight material such as glass fibre or long-haired wool is used, it may be laid directly on the membrane. When using acoustic absorbers above the membrane we prefer to use a perforated or porous structure so that where a coating is applied to the non-woven fabric, this coating may have a microporous structure, or it may be punched after coating to provide a large number of very small holes which are not normally visible in use, and which suitably occupy about percent of the total area of the membrane. Similarly, inherently non-porous materials such as plastic foil are also preferably perforated.

Because of the high dimensional stability of nonwoven fabrics made from composite filaments such as Cambrelle, and also because of the low stretch which is required, removable panels may readily be incorporated into the membrane. These may be secured by any convenient method depending on the degree of visibility permissible while retaining visual appeal, and suitable methods including lacing, Velcro" strip, zips, and hooks and eyes. Generally, the panel itself is come niently of the same material as the remainder of the membrane. The hatch so formed may provide access to the soffit, and is particularly useful where only a small hole is frequently required, access being afforded even more simply than by unhooking the main ceiling panel. in a similar manner, a translucent panel may be inserted into an otherwise opaque ceiling.

For rigid or semi-rigid panels having means for lateral location, it may not even be necessary to secure them to the membrane. We found that a lightweight diffuser of about 5 cm depth having an outwardly extending flange would rest in a hole therefor in the membrane, supported on itsflange. Even such a shallow article did not show any inclination to become dislodged by, for example, pressure changes due to the opening of doors.

The combination of the track and individual suspension members provides a very versatile system which can be made to give very even loading on the membrane even with shapes which provide difficulties for one or more of the previously known systems. Thus edge shapes may be readily provided having internal corners, even when such corners are repeated over short distances, as required for example around structural elements such as boxed-in girders. The edges may found where a ceiling of a lower floor meets that of an ascending staircase, we prefer to provide a rigid rail extending between the tracks on either side of the membrane. The membrane thus passes over the rail, being pulled tightly against it. For membranes undergoing such acute bends, we particularly prefer to use the nonwoven fabrics formed from Cambrelle and like filaments, on account of their greater stiffness in comparison to polyvinyl chloride foil. The foil clings closely to rail surface. The non-woven fabrics, on the other hand,

' tend to show surface details to a far less extent, while still providing a suitably abrupt change of direction.

Various decorative effects may be produced, either by varying the fabric from which the membrane is made, or by subsequently applying a decorative finish to its surface. For example, non-woven fabrics formed from Cambrelle composite filaments are available in a variety of surface finishes. The fabric may alternatively be passed between embossing rolls. Decorative patterns may be applied to the surface, for example as markings in the fire retardant surface coating such as wavy lines, or a series of short transverse lines by means of an oscillating rod or a cog wheel applied to the coating before the latter dries. Alternatively the coating may be sprayed or spattered with pairnt or other pigment, conveniently as the fire retardant coating is dried.

The fire retardant coatings described above are illustrative of a class of suitable compositions. These may be further modified by the addition of wetting agents, colourants, or moisture stabilisers for the ammonium bromide. Alternatively, coatings based on polyvinyl chloride latices may be used.

Having illustrated the invention by reference to a ceiling formed from a single panel, and discussed suitable variations and modifications, we now turn to further embodiments which have the same general features, but which comprise two or more discrete demountable panels.

The ceiling illustrated in FIG. 8 has a peripheral track formed from standard conduit tubing 81 secured to the walls 82 of a rectangular room by books 83 screwed into the walls at intervals around the periphery of the ceiling. The tubing 81 illustrated runs along one wall of the rectangular room, further tubing being likewise secured to the other walls to complete a continuous rectangle of track. The area of the rectangle so formed is subdivided by further lengths of conduit 81;, 81" extending the full width of the rectangle, but which are not attached at their ends to the main rectangle, these further lengths of conduit being suspended from the soffit 84 by flexible wires 85. The flexible wires are spaced apart along the conduit at approximately equal intervals of 3 m, the tubes so suspended being free to swing towards and away from the other tubes-parallel to them.

Stretched across the areas bounded by the conduit tubes, are parallel strips 86, 86', 86" of the ceiling membrane formed from a melded non-woven fabric formed from a mixture of polypropylene monofilaments and heterofilaments having a core of polypropylene sheathed with a layer of polycaprolactam, the fabric weighing about 3.3 g m*. The fabric has an opaque fire retardant coating applied by passing the fabric through a latex containing ammonium bromide, and allowing the adhering latex to dry.

There is a sewn hem around all sides of each strip of fabric, and rods 87 about 3 m long are threaded along the hems substantially end-to-end, the hems having been cut as required to allow the rods to be inserted. The edges of each membrane are attached to their ad jacent conduit 81, 82', 8!" by generally S-shaped hooks 88 looped around both the conduit tubes and the rods 86 within the hems of the membranes, the membranes being pierced as required by the hooks on assembly. During erection of the ceiling, the membrane fabric was stretched by only about 2 percent, but there is no readily apparent sag despite a minimum span for each panel of approximately 4.5 m.

Around the edges are extruded strips of white polyvinyl chloride providing a coving 89 which conceals the track 81 and hooks assembled therealong. To conceal the join between each pair of adjacent panels is a cover strip 810, also extruded from polyvinyl chloride, having two inward-facing lips 811 extending the full length of its concealed surface. Mounted on that surface are a plurality of spring clips 812, injection moulded from Kematal acetal copolymer, spaced apart at intervals along the full length of each strip. Each clip has two outward facing lugs 813 on its base, and is mounted on the strip by inserting the base of the clip between the two lips of the strip, and then rotating the clip so that the lugs engage behind the lips to retain the clips in sliding engagement. The strips are retained in place over the join by the clips being in snap engagement around the conduit, the conduit in turn preventing rotation of the clips which might otherwise disengage them from the strip.

We normally prefer to use the ceiling material in the form of long strips, the ends of which are connected to the track secured to the basic building structure around the periphery of the ceiling. However, this is not essential, and inner panels may have one or more panels adjacent each edge. This may be useful where changes in the plane of the membrane are required, e.g., where one area is required at a higher level than the remainder. However, where the requirement is merely one of access at one position, we prefer to use the smaller hatches secured by zips and the like as described hereinabove, provided the membrane is formed of a suitable material, e.g., the preferred non-woven fabrics.

The present means of joining adjacent panels may be advantageous where particularly large spans are required, in that support may be provided at intervals across the span, and a ceiling with negligible sag may be provided without the necessity for undue tension in the membrane. The membrane tension, however, may be balanced to some extent against the load on the wires 85. For example, during development of the present invention, it was desired to erect a ceiling below a roof structure considered to have insufficient strength to support a suspended ceiling of the exposed grid type, in which ceiling tiles would have been supported by a grid suspended from the roof structure. However, we found we could successfully suspend a ceiling constructed according to the present invention when formed from three strips of fabric about 4.2 m, 3.9 m and 3.9 m wide respectively. Conduit was used for both the peripheral track and the track running along the joins. The membranes were stretched with about a 1.3 percent extension, and it was found that the supporting wires were only lightly loaded on account of the weight taken by the peripheral track, and the loading thus produced was well within the safe limits for the roof structure. Although an extension of only about 1.3 percent was used successfully in the above experiment, in practice we would now generally prefer to use a slightly greater extension, e.g., 2 percent.

The use of several individual panels increases the versatility of the ceiling in that they may be readily removed and subsequently replaced. This may be of value, for example, where access to extended lengths, e.g., of serivce ducts, is required, or where rearrangement of department stores, factory areas, exhibitions or the like, requires alteration in ceiling height, slope or arrangement.

The intermediate track shown in FIG. 9 is formed from commercially available trunking comprising a channel section having a base 91 and two sides 92. The trunking is suspended from a soffit (not shown) on a rod 93, with the two sides downwardly directed from the base 91, being supported on the rod by a nut 94. The lower edges of the sides have inwardly directed, longitudinal lips 95.

Suspended horizontally from the trunking are two panels of ceiling membrane (of which only edge regions are shown), each of which panels has a hem 97 along its edge. Within each hem are a plurality of 3 mm diameter rods 98, placed end to end, and the membrane is attached to the track by a plurality of spacedapart hooks 99 engaging the rod 98 at one end and the lips at their other end. The means of suspension of the panels is concealed by a cover strip 910 which clips onto the lips 95.

The peripheral track of FIG. 10 is formed from trunking having the same channel section as that used for the intermediate track shown in FIG. 9, and like numerals denote like parts. The trunking is secured to a wall 100 of the basic building structure by a screw 101. The means used to suspend the membrane is again covered by a cover strip 102, having a shape similar to that 910 shown in FIG. 9, except that on one side it does not extend so far.

An alternative method of securing the channel to the wall is to drill an oversize hole through the side of the channel attached to the membrane so that the fixing screws pass directly through the oversize hole and engage only the side remote from the membrane. This avoids the risk of the fixing screws closing the channel and preventing the cover strip from being inserted, but this also prevents the screw itself being used to combat the tendency for the membrane tension to open the channel.

A further alternative method of securing channel trunking to the wall is to use square L-shaped hooks threaded on one leg so as to be screwable into the wall, the other leg being turned to extend upwards, spaced away from the wall so as to provide a recess therebetween. The channel is then mounted on the wall simply by slipping the side of the channel adjacent the wall, into the recess. With some sections of channel, particularly those having large inwardly extending flanges, further useful support may be obtained by the use of timber wedges between the upwardly extended legs of the hooks and the inner surface of the channel.

FIG. 11 shows an alternative peripheral track having the same shape as half of the trunking used in FIG. 10 in that the side 111, the flange 112, and the base 113 are again present in the same shape as before. The track differs, however, in having an upwardly extending lug 114 for securing the track to a wall by means of screws 115. The membrane edge detail is the same as before, but the suspension hooks 116 are S shaped. These are alternative to the C" shaped hooks shown in both the previous Figures and either may be used as desired in each case. The coving illustrated is different from that of FIG. 10 in that it has two functionally distinct regions, i.e., a vertical portion 117 which is screwed to the wall, and a concealing portion 118 connected to the vertical portion by a hinge 119. When the ceiling has been erected, the concealing portion is folded upwards at the hinge so that the resilient upstand 1110 clips over the flange to support the concealingportion in a horizontal position.

Where a multiplicity of individual suspension members are used to directly interconnect adjacent panels, i.e. in the absence of an intermediate track, with some (at least) of the members suspended from the soffit, the members may be shaped substantially as illustrated in the accompanying drawings, with the symmetrical shapes (e.g., as shown in FIGS. 9 and 10) being preferred. The members may be suspended from the sofflt by a flexible wire in a manner similar to the suspension of the track shown in F l0. 8. The members may be provided with a loop or other integral shape intermediate the end hooks, to assist in attaching a suspending wire to the member.

We claim:

1. A suspended ceiling comprising a track secured to a basic building structure around the periphery of the ceiling, and a flexible membrane attached at its edges to the track by a multiplicity of individual attachment members extending outwards from spaced-apart points along said edges and engaging the track so as to be movable therealong, the membrane being maintained thereby in a stretched condition across the area defined by the track, a covering being secured below the edges of the ceiling so as to conceal the attachment members and track.

2. A ceiling according to claim 1 in which the track is formed from a plurality of tubular members arranged end-to-end around the periphery of the ceiling.

3. A ceiling according to claim 1 in which the track is secured to the basic building structure by a plurality of hooks shaped to receiving the track, said hooks having a threaded shank for attachment to the basic structure.

4. A ceiling according to claim 1 in which the attachment members have a hook-shaped end for engaging the track and are hook-shaped at their ends remote from the track.

5. A ceiling according to claim 1 in which the membrane has an edge and said edge has a part provided with inextensible reinforcing members secured thereto in such a manner as to prevent said part from stretching, wherein the total length of said part is less than percent of the length of said edge.

6. A ceiling according to claim 1 in which the membrane has along each of its edges a hem providing a pocket within which is slidably located one or more rods positioned with respect to the attachment members such that the tensile forces stretching the membrane are applied by the attachment members to the rods, said forces being thereby spread along the edge of the membrane.

7. A ceiling according to claim 1 in which the membrane is formed from a melded fabric comprising filaments having a core of polypropylene sheathed with a layer of polycaprolactam.

8. A ceiling according to claim 1 in which the attachment members comprise a plurality of hooks having ends extending downwardly through the membrane, said ceiling having a coving which comprises a resilient elongated strip having on one surface a ridge extending longitudinally therealong and an upstand projecting out of the ridge and extending therealong such that a recess is provided between the upstand and said surface, whereby on presenting said surface towards the track so that said ends of the hooks enter the recess and engage the upstand, the two longitudinal edges of strip are sprung against the membrane and basic building structure respectively.

9. A ceiling according to claim 1 which is formed from a plurality of discrete panels of the flexible membrane; the ceiling having in addition to the track around the periphery, intermediate track located between adjacent panels, the panels being attached to the intermediate track by a multiplicity of individual attachment members.

10. A ceiling according to claim 9 in which the intermediate track has an inverted channel section comprising a base with two downwardly directed sides, each having an inwardly directed lip extending along its lower edge, the panels being attached to the intermediate track by a multiplicity of individual attachment members spaced apart along an edge of each panel and hooked around the adjacent lip of the track.

11. A ceiling according to claim 1 comprising a plurality of adjacent panels directly interconnected by a multiplicity of individual suspension members, at least some of which are suspended from an overlying soffit.

12. A ceiling according to claim 1 in which the attachment members comprise a plurality of hooks having ends extending through the membrane, the coving comprising a resilient elongated strip having on one surface at least one ridge extendigg lor itudinaly therealong, said ridge being adapted to engage said hooks and thereby retain the coving in position.

13. A suspended ceiling according to claim 1 in which the membrane is formed from a melded fabric coated with a flexible opaque latex.

14. The combination adapted for use in providing a suspended ceiling as claimed in claim 1, comprising said flexible membrane and said multiplicity of attachment members, the attachment members being hookshaped to engage the membrane at spaced apart points along its edge and also shaped to engage the track so as to be movable therealong and the membrane being cut to size and its edges adapted to receive said hooks.

UNITED s1 TES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No. 3,824,080 Dated October 29. 1974 Inv n M James Mgliarhne Bro Adrian Marden and Arthur Christoper Pancewicz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Page 1, at 1005: 30, insert -Sept. 9, 1970 Great Britain 43152/70 Page 1, at box 63, "Sept. 8" should read --Sept. 9--.

Signed and sealed this 13th day of May 1975.

(SEAL). v Attest:

- C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer I a and Trademarks UHIDMM-nc mnInq-n; I \ll minimumrumnutmu-l nu u. I

7 OHM I'D-I050 H0419)

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Referenced by
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US4739592 *Jun 24, 1986Apr 26, 1988Baguena Molina Maria Del PilarProtective awning for scaffolding and tubular structures
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Classifications
U.S. Classification52/222, 52/509, 52/506.6, 52/511
International ClassificationE04B9/30
Cooperative ClassificationE04B9/303
European ClassificationE04B9/30B