THE PRESENT INVENTION relates to thermally insulating glazing-

It has been proposed to provide thermally insulating glazing, one example being the increasingly conventional double glazing used on windows in domestic houses. However, thermally insulating glazing is used in other applications, and in particular is utilised in conjunction with certain types of solar energy collector.

Such thermally insulating glazing forms the top part of a housing constituting a solar collector. A chamber, within the housing, located beneath the thermally insulating glazing is raised to an elevated temp¬ erature by the action of sunlight falling on the solar energy col lector. The thermal ly insulating glazing assists in maintaining as high a temperature as possible within the appropriate chamber.

It has, of course, been proposed to utilise in this context a glazing arrangement consisting of two layers of glass, slightly spaced apart. This arrangement suffers from a disadvantage that only between 84 and 92% of the energy fal ling on a sheet of glass in the form of sunlight actually passes through the glass. The rest of the energy is lost either by reflection or by transmission losses. Thus, when the sunlight has to pass through two layers of glass a substantial proportion of the energy initially available to the solar energy collector is lost before the light has passed through the glazing arrangement.

It has been found that up to 97% of the energy present in sunlight can pass through a foil of transparent plastics material, such as a film of polytetrafluoroethylene as sold under the Registered Trade Mark TEFLON. Thus it has generally been proposed to utilise a thermally insulating glazing arrangement consisting of one layer of glass and one layer of such a thin transparent plastic film.

Attempts have been made to stretch the foil of plastic film on a frame that supports the sheet of glass and also on a separate frame spaced slightly from the frame that supports the glass. However, it has been found that when such a plastics material foil is subjected to a high temperature, the foil effectively expands, and thus looses tension and sags. Since, in utilising such a thermally insulating glazing arrangement, the sheet of glass will be on the outside and the sheet of foil will be on the inside, when the thermally insulating glazing is used with a solar collector, as mentioned above, the foil will be subjected to the high temperature, and will thus sag.

I Q As a result of the effects of static electricity the foil may then cling to the glass.

Attempts have been made to support the foil on an open wire mesh. Thus only relatively short lengths of foil are unsupported, thus tending to ι c minimise the degree to which the foil can sag, even if the foil does expand.

However, the presence of the wires does tend to reduce the amount of energy that can be usefully collected by the solar energy connector, and also the wires can actually cut the foil, which is clearly disadvantageous.

20 The present invention seeks to provide an improved thermally insul¬ ating glazing arrangement.

According to this invention there is provided a thermally insulating glazing arrangement, said arrangement including a rigid sheet of transparent

25 material (such as glass) and spaced therefrom, a thin film of transparent plastics material, means being provided to maintain tension in the thin film of plastics material even if it expands thermally.

Preferably the thin film is mounted in position on at least one 3Q resilient member, the resilient member being deformed so that the resilient member imparts tension to the film.

Conveniently the resilient member is in the form of an elongate flange extending substantially perpendicularly to the plane of said rigid 35 glazing material.

Advantageously said resilient member is mounted on a frame separate from the rigid glazing material.

Preferably the resilient member is connected directly or indirectly to said rigid glazing material.

Conveniently the resilient member is formed as part of a bead, the bead being mounted on the edge of the rigid sheet of transparent material.

Preferably the resilient member is formed of a rubber or rubber-like material.

In one embodiment the glazing arrangement is fabricated by locating two beads in position, on two opposed edges of the rigid sheet of transparent material lightly stretching the film across the beads and securing the edges of the film in position and subsequently applying pressure to part of the film in order to deform said resilient members on the beads so that they apply tension to the film.

Preferably the film is initially adhered to edges of the beads perpendicular to the plane of the glass and subsequently pressure is applied to parts of the film between said adhered portions and the regions of the • ilm touching the resi lient members so that said portions of the film are brought into contact with the bead, thus' deforming the resilient members.

Conveniently the said film is deformed in such a way that it is adhered to the bead.

The film may be deformed when the glazing assembly is inserted into a supporting frame.

Preferably said frame defines a seat and the glazing assembly is retained in position in the seat by means of retaining strips held in position by screws or the like.

Said glazing arrangement may form part of a triple or quadruple glazing assembly.

According to another aspect of this invention there is provided a thermally insulating glazing arrangement, said arrangement comprising a

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sheet of rigid glazing material, beads mounted on at least two opposed edges of said sheet of glazing material, deformable resilient members mounted on said beads and extending away from the plane of said sheet of glazing material, a thin film of transparent plastics material being located over said protruding resilient members and being secured in position in such a way that the resilient members are deformed to apply tension to the film of plastics material, the thin film of plastics material being retained in spaced parallelism with the sheet of glazing material.

Preferably the thin film of plastics material is a thin film of polytetrafluorethylne.

Conveniently said thin fi lm of plastics material is adhered to the said beads to retain the film in position.

According to a further aspect of this invention there is provided a method of fabricating a thermal insulating glazing assembly, said method comprising the steps of taking a sheet of rigid glazing material, mounting beads, on at least two opposed edges thereof, each bead carrying a deformable resilient element extending away from the plane defined by the sheet of rigid glazing material, loosely stretching a form of transparent plastics material across said resilient members,and securing the film in position in such a way that the resilient members are deformed to retain the film under tension in spaced parallelism with the sheet of rigid glazing material.

Preferably the film is adhered to the beads to retain the film in position.

Conveniently the film is initially adhered to one part of the bead, whilst the film is under relatively light tension, and is then subsequently adhered to another part of the bead, thus deforming the said resilient elements.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which:

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FIGURE 1 is α sectional part perspective view of part of a glazing arrangement in accordance with the invention whilst it is being fabricated,

FIGURE 2 is a cross sectional view through the arrangement of Figure I at a subsequent stage of fabrication,

FIGURE 3 is a view corresponding to Figure 2 at the next subsequent stage of fabrication,

FIGURE 4 is an exploded view showing the arrangement of Figure 3 being inserted into a permanent frame,

FIGURE 5 is a cross sectional view of one rubber bead that may be uti lised in performing the invention, and

; 5

FIGURE 6 is a cross sectional view of another form of rubber bead that can be uti lised in performing the invention.

Referring initially to Figure I of the accompanying drawings, in 0 forming a thermally insulating glazing arrangement in accordance with the invention initially a rigid sheet of glass I is taken, although it may be practicable to utilise a rigid sheet plastic material.

As shown in the drawing, strips of rubber bead 2 are engaged with the ς four edges of the sheet of glass I . Each bead has a portion 3 defining a substantially U-shaped channel 4 dimensioned to engage the edge of the sheet of glass as a friction fit. Adjacent the mouth of the channel the bead defines a protruding resilient flange 5, the flange 5 extending, as shown in Figure I , substantially perpendicularly to the plane of the glass sheet I . As 0 will become apparent hereinafter, the flange 5 is resilient.

In the region of the corners of the sheet I each flange 5 is bevel led, 6, for a purpose that will become clear hereinafter.

35 Illustrated in Figure I is a film 7 of thin transparent plastics material, such as a thin film of polytetrafluorethylene as sold under the Registered Trade Mark TEFLON. The film 7 of plastics material is to be

secured to the remaining above-described elements to form a thermally insulating glazing arrangement.

The first step of securing the film 7 in position is to provide the outer surfaces 9, 10 of each bead with an adhesive coating material. The film 7 is then lowered on top of the glass 1 with the associated beads 2, so that the film rests on the upstanding f langes 5. With the application of a slight amount of tension, so that the film is reasonably tight, the film is then pressed against the side faces 9 of the beads, and is thus adhered to those faces. The condition illustrated in Figure 2 is then obtained with the film extending from the side face 9 of the bead 2, as shown at the left of the figure, angularly to the top of the flange, substantially horizontally parallel with the sheet of glass 1 , and angularly down from the flange 5 at the right hand side of the figure, to the side face 9 of the bead 2 shown at the right hand side of the figure. By applying pressure as indicated by the arrows 1 I shown in Figure 3 the angularly extending portion of the film 7 between the face 9 and the flange 5 of each bead is pressed downwardly to contact with the surface 10 of each bead, and since the surface 10 has been coated with adhesive, the film is adhered thereto. As the film is pressed down in this way the tension in the film increases and the resilient flanges 5 are bent inwardly, as shown in Figure 3. Since the flanges are resilient, the flanges thus exert a bias on the film 7 tending to maintain tension in the film.

It will be appreciated that when the flanges bend inwardly, as shown in Figure 3, in the regions of the corner of the sheet of glass I , as a consequence of the provision of the bevelled portions 6, the flanges do not interfere with each other.

The thermally insulating glazing assembly, as shown in Figure 3, may then be inverted and may be inserted in a supporting frame, as shown in

Figure 4.

The frame 12 may be formed of any suitable material and defines a seat 13 adapted to receive the thermal ly insulating glazing assembly. The assembly unit may be retained in the seat by means of retaining strips 14 held in position by means of screws 15 but, of course, many other possible arrangements could be utilised.

Of course, this insertion step may actually perform the pressing in the direction of the arrows 1 1. The frame abutting the beads wil l assist in keeping the film adhered to the beads.

The frame 1 2 may form part of a solar energy collector, and the arrangement may be such that the film 7 is, in use of the arrangement, subjected to a high temperature.

It will be appreciated that if the film 7 is subjected to a high temperature the film will tend to expand. However, when the film expands the resilient flanges 5 will tend to move back towards their initial condition, i.e. they will tend to move from the inclined position as shown in Figure 3, to the position in which they are perpendicular to the plane of the glass as shown in Figure 2. Thus the resilient flanges 5 wil l always maintain the film 7 under tension, thus preventing the film from sagging and also preventing the film from being drawn into contact with the glass by electrostatic forces.

It will thus be appreciated that since, in the described arrangement, there is a resilient element which is initially deformed so that it applies a tension to the plastics film 7, even if the plastics film expands the resilient element will maintain tension in the film, thus preventing the film from moving from its desired position.

It is to be appreciated that whilst one particular design of bead has been il lustrated in figures 1 to 4 for the purposes of explanation, many different types of bead could be utilised. For example, as shown in Figure 5, which shows a bead 2 ¹ the f lange 5' could be of a tapering configuration. In such a case the tip of the flange would tend to bend more than the base of the flange, and thus when the film is under tension each flange wil l tend to be bent in an arcuate manner.

Figure 6 illustrates another bead 2" where the flange 5" is of significant length. In utilising such a bead the film 7 wil l be spaced a considerable distance from the plane of the glass I , but nevertheless will be retained under adequate tension to keep the film relatively taut.

The precise properties of the resilient flange will depend upon the design of the flange and the resilience of the rubber or other material from ^' which the bead and flange are made.

Whilst the invention has been described with primary reference to a solar energy col lector it is to be appreciated that a thermal ly insulating glazing unit as described above may be utilised as part of a triple glazing arrangement or as part of a quadruple glazing arrangement. As wil l be appreciated, in normal thermal insulating glazing as used in houses or the like, it is necessary to have a sheet of glass on the outside of the thermal insulating glazing, since this part of the glazing will be subjected to the effect of wind, rain, snow etc, and it is also desirable to have a sheet of glass or other rigid glazing material on the interior of the thermally insulating glazing arrangement. However, it will be understood that if one of the sheets of glass present in a conventional double-glazed arrangement is replaced by a thermally insulating glazing assembly a structure as shown in Figure 3, with the thin film 7 being located between the two sheets of glass of the double glazing arrangement, effectively a triple glazing arrangement is provided, the central glazing element being constituted by the thin film 7. A quadruple glazing unit can be made from two assemblies as shown in Figure 3. This may well prove to be very advantageous, especially since the thin film 7 transmits virtually al l the light falling on it, there only being minimal reflection and transmission losses.

Of course, thermal insulating glazing arrangements in accordance with the invention may find many different applications and may thus, for example, be utilised as windows at elevated positions, for example in factories, in which case it may be necessary for the thin film of plastics material to be replaced at regular intervals. It may be cheaper, however, to replace the plastics material film, rather than to clean ordinary glazed windows, especially if the factory is utilised to perform a dirty process, or, for example, if paint spray can fall on the windows.

Whilst the invention has been described with reference to one particular embodiment, many different arrangements can be envisaged within the scope of the invention. It is not necessary for the resilient member that applies the tension to the film to be mounted directly on the

glass sheet, since the resilient member could be mounted on a supporting frame or could be mounted in some other way.

Whilst the described resilient member is in the form of an unbroken flange, it is to be appreciated that the resilient member could be constit¬ uted by a plurality of separate resilient fingers, for example.

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