Numerous forms of frames for this purpose have been utilized and invariably consist of a series of parallel main runners supporting at intervals parallel cross runners to produce rectangular openings defined by the runners for accommodating ceiling lining panels, or tiles. The runners have lower co-planar flanges for support of the lining panels. In so-called concealed suspension systems the panels have recessed edges and accommodate the flanges, but in the more popular form of exposed systems the marginal edges of the panels merely overly the flanges on the runners. It is of aesthetic importance that there be a minimum of gap between the flanges of the cross runners and the main runners, and that the entire frame, when assembled, be as rigid as possible. In some instances separate keys are used to connect cross runners to the main runners via slots in the latter, and even where locking tongues are provided on the former the task of accurately locating these tongues into the slots can be tedious for installation personnel.

DISCLOSURE OF THE INVENTION It is the main object of the invention to provide a frame construction for a ceiling suspension system which, at least in the above respects, is an improvement on previous forms. In accordance with the invention there is provided a frame for support of ceiling panels in a ceiling suspension system comprising at least two parallel spaced main runners and a cross runner bridging said main runners, wherein each of said main runners has an upper flange for engagement by suspending means of said system and a lower flange for holding said ceiling panels, and a vertical web interconnecting said flanges and provided with an aperture, and wherein said cross runner has a lower flange, an upright web connected thereto, and longitudinally extending tongues at opposite ends for engagement within the apertures in the webs of the main runners for location and support of the cross runner; said frame being characterized in that each of said main runners is formed from sheet metal strip folded about its longitudinal centreline to create said upper flange, outwardly and folded near its opposite longitudinal edges to create said lower flange lateral marginal portions of said strip,

and so that said web is formed of double-wall construction with an internal longitudinal space between the walls extending from the upper flange to near said lower flange; and being further characterized in that said tongues on the cross runner have an upwardly extending terminal tooth and a lower abutment relatively spaced so that when the tongue at one end of said cross runner has been inserted through said aperture in one of said main runners with said tooth adjacent the outer face of the far wall of the web the lower flange of the cross runner is brought co-planar with the lower flange of the main runner by force applied to overcome resiliency of the metal walls of the web due to said tooth engaging said outer face of said far wall and said abutment bearing upon the outer face of the near wall of the web.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawing showing in perspective a main runner and a cross runner of this invention in preparation of assembly.

BEST MODE OF CARRYING OUT THE INVENTION With reference to the drawing the main runner 1 and the cross runner 2 are of unique form. Although the latter is preferably composed of folded sheet metal, it is of essence that the main runner 1 be composed of sheet metal, preferably a strip 3 of galvanised mild steel. The strip 3 is processed by being folded along its longitudinal centreline to form an upper flange 4 on the runner 1 which is generally of rectangular, or oval, cross-sectional shape. The upper flange 4 is designed to be gripped by suspending means (not shown) secured to the underside of a horizontal supporting surface. The suspending means is of conventional form, requiring no further description herein. Folding of the strip 3 forms a double walled web 5 to define between the opposite walls 6 and 7 a longitudinally extending space 8. The opposite lateral marginal portions 9 and 10 of the strip 3 are outwardly flared in opposite directions from the bottom of the web 5 by further folding near the longitudinal edges of the strip 3 to form part of a lower flange 11 on the runner 1. A colour bonded cover strip 12 has its lateral edges folded over the extreme edges of the marginal portions 9 and 10 of the strip 3 and is firmly clamped thereon. Longitudinally extending locating ribs 13 and 14 may be provided upon the marginal portions 9 and 10 for accurate location of the strip 12. Preferably, the internal space 8 between the walls 6 and 7 of the web 5 tapers downwardly from the upper flange 4 to near the lower flange 11 where

the two walls 6 and 7 come in contact with each other. A series of vertical slots, such as slot 15, are punched through both walls 6 and 7 of the web 5 at intervals along its length.

The cross runner 2 is also preferably formed from a strip of galvanised mild steel and folded along its longitudinal centreline to create a small reinforcing rib 16 along the upper edge of the runner 2, and to form a double walled web portion 17, and lateral marginal portions 18 and 19, over which is folded and crimped a colour bonded cover strip 20 of similar form to the strip 12, to create a lower flange on the runner 2. Longitudinally extending tongues 21 are provided at opposite ends of the runner 2 and each support an upstanding, terminal tooth 22. A somewhat arcuate end is provided on the tongue 21 between the tooth 22 and an abutment 23. It will be noticed that the tongue 21 is narrower than the main body of the cross runner 2, and it is arranged that the width between the upper edge 24 of the tongue 21 and the abutment 23 is slightly less than the length of any of the slots 15. Furthermore, the width of each slot 15 slightly exceeds the combined thickness of two tongues 21 to permit engagement within the same slot 15 of tongues 21 from cross runners 2 entered from opposite sides of the main runner 1. Also the end portions of each runner 2 are pinched together along the press line 25 to ensure that each tongue 21 is of double thickness without any intervening space. Longitudinally extending reinforcing ribs 26 are also pressed into each tongue 21.

By the above-described construction assembly of cross runners 2 to main runners 1 is greatly simplified, as with inclination of a cross runner 2, as shown in the drawing, to a fixed main runner 1 an end tongue 21 may be passed longitudinally along part of the length of the runner 1 until the tooth 22 slips into a selected one of the slots 15 for correct location of the cross runner 2. Should the outer end of the runner 2 then be lowered towards the plane of the lower flange 11 of the main runner 1, the tooth 21 will move towards engagement with the outer face of the far wall 6 of the web 5 due to the cam-like engagement of the arcuate end of the tongue 21 with the bottom of the slot 15. Further downward movement of the outer end of the cross runner 2 brings the abutment 23 into engagement with the outer face of the near wall 7 of the web 5, immediately below the slot 15. The relative positions of the tooth 22 and the abutment 23 upon each tongue 21 is such that when both initially engage with their respective walls 6 and 7 of the web 5 the lower flange of cross runner 2 remains short of the plane

of the lower flange 11 of the main runner 1, requiring the application of force to achieve co-planar alignment, and this is permitted solely through the resiliency existing between the walls 6 and 7 of the web 5. As a result exceptionally firm assembly is achieved with a minimum of a gap existing between the lower flanges of the two runners 1 and 2. It has been found that due to the space 8 provided in the web 5 and the resulting resiliency between the walls 6 and 7, good firm assembly and absence of gaps between lower flanges is achievable despite rather wide manufacturing tolerances. Whereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms, modifications and refinements are feasible within the scope of this invention.