GB2117427A

GB2117427A - Suspended ceilings

Info

Publication number: GB2117427A
Application number: GB08308462A
Authority: GB
Inventors: Robin Anthony Ernest Desbois
Original assignee: Armstrong World Industries Ltd
Current assignee: Zentia Ltd
Priority date: 1982-03-26
Filing date: 1983-03-28
Publication date: 1983-10-12
Also published as: GB2117427B; GB8308462D0

Abstract

A cover for a light fitting in a suspended ceiling 16 to 20 comprises a horizontal sheet of transparent plastics material 1 in a frame comprising a vertical web 4, a first flange 3 on which the sheet 1 rests, a second flange 5 under which the sheet 1 fits, and a third flange 6 which together with the web 4 and the second flange 5 forms a C-section channel by which the cover is attached by supports 9 to 15 to the suspended ceiling. <IMAGE>

Description

SPECIFICATION Improvements in and relating to suspended ceilings The invention relates to suspended ceilings, and especially to light-scattering covers for light fittings mounted in such ceilings.

It has for many years been known to mount light fittings in rooms with suspended ceilings above the level of the suspended ceiling and to provide transparent or translucent panels in the ceiling to allow the light through into the room below. If the panels were transparent, they often had a patterned surface, for example, in the form of an array of prisms or pyramids, to improve the distribution of light into the room. Such panels have in the past been mounted in the ceiling by resting them on the flanges of L-section or inverted T-section frame members. This arrangement was simple, but it has been found that the panels tend to rattle on the frame members, for example as a result of updraughts present in the room.More seriously, it has been found that a sudden downdraught, for example, as a result of a door being closed, could cause the panel to bow downwards to the point at which it fell completely out of its frame. In recent years, the transparent or translucent panels have been made of increasingly thin, and thus increasingly flexible, plastics material in order to reduce costs, with the result that these problems have become increasingly important. The problem is especially great with panels having one surface formed into an array of prisms, because the stiffness of the panels is then determined largely by the thickness of the continuous layer of material between the back face of the panel and the bases of the pyramids, which is of course less than the overall thickness of the panel by the height of the prisms.This problem is exacerbated by the fact that, in order to reduce the amount of material used still further, the proportion of the thickness of the panel occupied by the pyramids has been increased so that even with a panel of a given overall thickness the stiffness has decreased.

The invention provides a cover for a light fitting in a suspended ceiling, comprising a sheet of light-transmitting material that is generally horizontal in normal use, a frame substantially surrounding the sheet and comprising a first flange extending inwards adjacent to the bottom face of the sheet, a second flange extending inwards adjacent to the top face of the sheet, and a vertical web connecting the two said flanges, the thickness of the said sheet being substantially equal to the gap between the two said flanges, and means including a part of the web above the said sheet for mounting the cover in the suspended ceiling.

Preferably, the cover comprises a third flange extending inwards from the web above the second flange, and wherein there are provided lips on the inner edge portions of the second and third flanges extending towards each other, the second and third flanges, the said lips, and the part of the web joining the second and third flanges together forming a channel of C-shaped cross section substantially encircling the cover above the said sheet, and wherein the mounting means comprises the C-shaped channel.

The presence of the second flange can effectively prevent the sheet from rattling in its frame, because even if the sheet is significantly thinner than the width of the gap between the first and second flanges, for example, the sheet may exceptionally be as thin as 2.5 mm if the gap between the flanges is 3 mm, the sheet cannot usually buiid up enough kinetic energy to provide an unacceptable volume of noise. Also, because the outer edges of the sheet are held down it cannot bow downwards nearly as easily as in previously proposed frames with the sheet merely resting on a flange, greatly reducing the risk that it will be pulled out of the ceiling.Furthermore, because members supporting any joints in the frame and the means for mounting the cover in the ceiling can be arranged in or on the C-shaped channel, above the edge portion of the light transmitting sheet, virtually the entire width of the first flange can be used to support the sheet, which was often not possible with previous designs, where joints often has to be reinforced by angle brackets or the like fitting between the edge of the sheet and the vertical webs of the frame members being joined.

One form of cover for a light fitting in a suspended ceiling will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary cross-sectional view of the cover and part of the ceiling surrounding it; Fig. 2 is a fragmentary section along the line X-X of Fig. 1;and Fig. 3 is a view similar to Fig. 1, showing an alternative form of mounting for the cover.

Referring to the accompanying drawings, and initially to Figs. 1 and 2, one form of light cover for use in a suspended ceiling comprises a rectangular sheet 1 of light-transmitting plastics material, for example, clear polystyrene sheet with its lower surface formed into an array of elements of generally pyramidal form and having quadrilaterai bases. Such a sheet may have an overall thickness of 3 mm, the pyramids occupying up to 2 mm of that and their bases being, say 5 mm on a side.

The plastics sheet 1 is mounted in a frame consisting of four lengths of aluminium alloy extrusion indicated generally by the reference numeral 2 with mitred corners. The extrusion 2 comprises a horizontal bottom flange 3, on which the sheet rests, extending inwards from a vertical web 4, and a middle flange 5 and an upper flange 6 both extending inwards above the bottom flange. The sheet 1 rests on the bottom flange 3 over substantially the entire width, approximately 20 mm, of the upper surface of the flange, and is a substantially exact fit between that surface and the underside of the middle flange 5.

The middle flange 5 and the upper flange 6 have lips 7 and 8 that extend towards each other to produce, in conjunction with the upper part of the web 4, a generally C-shaped channel. The corner joints of the frame are held together by Lshaped angle brackets (not shown) positioned within the channel and clamped against the insides of the lips 7 and 8 by screws that engage in tapped holes in the angle brackets, the heads of the screws bearings, through washers if necessary, on the outsides of the lips 7 and 8.

The cover is supported by wire spring clips indicated generally by the reference numeral 9.

On a 60 cm square cover with the first form of mounting, as shown in Figs. 1 and 2, there are preferably four clips 9, one near each end of each of two opposite sides of the cover. Each spring clip 9 has a central loop 10 through which passes a screw 11. The screw 11 engages in a nut 12 captive within the C-shaped channel. The wire of the spring clips 9 is typically as much as 1 mm thick, so if the extrusion 2 is suitably proportioned no washer is necessary. Two arms 13 with looped ends 1 3a extend from the central loop 10 of the clip 9, and when the cover is in position they pass through a slot 14 in a bracket 1 5 and lie substantially flat against the upper surface of the bracket.The bracket 1 5 is generally L-shaped, and is mounted on a support member 1 6 of the suspended ceiling of inverted T crosssection with one limb of that L flat against the vertical web 17 of the support member and the other limb extending across and overhanging one of the horizontal flanges 18 of the support member. The slot 14 is in the overhanging portion of the bracket 1 5 and extends substantially parallel to the length of the support member 16.

Vertical slots 1 7a are provided at regular intervals in the web 17, and the brackets 1 5 are secured by screws 15a passing through these slots. The screws 11 may be slackened and the clips 9 slid along the C-shaped channel in order to align them with the brackets 1 5.

The outer face of the web 4 of the extrusion 2 is substantially in the plane of the web 17 of the support member 16. On the other side of the web 17 from the bracket 15 is a ceiling board 19, the edge face of which is formed with a groove 20 which receives the flange 18 on that side of the support member 16.

Referring now to Fig. 3 of the drawings, the second form of mounting is especially suitable for use on the long sides of a rectangular cover where these lie along Z-shaped support members of the suspended ceiling. The cover is substantially identical to that described above with reference to Figs. 1 and 2, but the arms 1 of each spring clip 9 pass through a slot 24 in a fixing clip 25. The clip 25 has a rectangular body portion 26 with the slot 24 in it, a central tongue 27 extending in the plane of the body portion from the centre of one side, and two outer tongues 28 extending parallel to the central tongue on either side of it and slightly out of its plane. The whole clip 25 may be stamped from a sheet.In use, the clip 25 fits on one bottom flange 29 of a Z-shaped support member 30, with the central tongue 27 extending across under the support member and digging into a ceiling board 1 9 on the other bottom flange 29. The outer tongues 28 fit over the flange 29. It will be noted that the bottom flanges 29 of the support member 30 are narrower than the bottom flanges 18 of the T-shaped support member 16, and accordingly the fixing clip 25 is arranged to support the spring clip 9 away from the edge of the flange 29. Also, the fixing clips 25 are not screwed to the support members 30 and thus may be inserted at any desired points along the sides of the cover.

The light fitting associated with the cover may be of a conventional light-weight type mounted on top of the support members 16 or 30.

In order to gain access to the light fitting, or to clean the plastics sheet 1, the cover is pulled downwards. In order to make this easier, the outer face of the web 2 is longitudinally fluted, the flutings 21 giving a purchase to the fingers of the person removing the cover. The flutings also have a decorative effect if the adjacent ceiling board 1 9 is shallower than the extrusion 2, and similar flutings 22 are preferably provided on the underside of the bottom flange 3. As the cover is pulled down, the arms 13 of the clips 9 are bent upwards and slide downwards through the slots 14 or 24 until the looped ends 1 3a catch on the ends of the slots. The arms 13 must be long enough that the cover is then hanging far enough below the plane of the ceiling that a finger and thumb can be inserted to pinch the arms 13 together and free the clip 9 entirely from the bracket 1 5 or the fixing clip 25. The cover may be removed entirely or, if the clips 9 on one side are left attached, may be tilted downwards for cleaning while still being partly supported. To facilitate this latter approach, hinges (not shown) may be provided for the clips 9 instead of the simple screws 11.

Claims

1. A cover for a light fitting in a suspended ceiling, comprising a sheet of light-transmitting material that is generally horizontal in normal use, a frame substantially surrounding the sheet-and comprising a first flange extending inwards adjacent to the bottom face of the sheet, a second flange extending inwards adjacent to the top face of the sheet, and a vertical web connecting the two said flanges, the thickness of the said sheet being substantially equal to the gap between the two said flanges, and means including a part of the web above the said sheet for mounting the cover in the suspended ceiling.

2. A cover as claimed in claim 1, which includes a third flange extending inwards from the web above the second flange, and wherein there are provided lips on the inner edge portions of the second and third flanges extending towards each other, the second and third flanges, the said lips, and the part of the web joining the second and third flanges together forming a channel of C shaped cross section substantially encircling the cover above the said sheet, and wherein the mounting means comprises the C-shaped channel.

3. A cover as claimed in claim 2, which is polygonal and wherein the frame comprises a frame member extending along each side of the polygon, the frame members being secured together by angle-brackets within the C-shaped channel at each corner.

4. A cover as claimed in claim 3, wherein the angle-brackets are clamped against the insides of the said lips by clamping means abutting against the outsides of the lips.

5. A cover as claimed in claim 4, wherein the clamping means comprise screws engaged in threaded holes in the angle brackets.

6. A cover as claimed in any one of claims 2 to 5, wherein the mounting means comprises a plurality of clip means each secured to the cover by a screw-threaded member engaging in a nut captive within the C-shaped groove.

7. A cover as claimed in claim 6, wherein each clip means comprises a resiliently yieldable portion that in normal use rests on an upper surface of a supporting bracket, and wherein the arrangement is such that the cover can be displaced downwards from its position in normal use against the resilience of the clip means.

8. A cover as claimed in claim 7, in combination with a plurality of supporting brackets each arranged to be secured to a support member of a suspended ceiling and provided with a portion that in normal use is generally horizontal and has in it a slot through which the resiliently yieldable portion of a clip means can pass.

9. A cover as claimed in any one of claims 1 to 8, wherein the lower surface of the sheet of lighttransmitting material is formed into an array of pyramids or prisms.

10. A cover as claimed in any one of claims 1 to 9, wherein the outer surface of the vertical web is provided with a plurality of horizontal ribs.

11. A cover as claimed in any one of claims 1 to 10, wherein the bottom surface of the said first flange is provided with a plurality of longitudinal ribs.

12. A cover as claimed in claim 1 and substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

13. A suspended ceiling having at least one light fitting positioned behind a cover as claimed in any one of claims 1 to 13.

14. A suspended ceiling substantially hereinbefore described with reference to, and as shown in, the accompanying drawings.

15. A set of parts for a cover as claimed in any one of claims 1 to 12 or a suspended ceiling as claimed in claim 13 or claim 14.