The size of box panels is often governed by the type of press used to produce the box tray. Steel panels produced for the Patera system (Fig. 6.34) were stamped out in three separate pressings for the same panel prior to fabrication into a composite unit using a mineral wool insulation core.
The type of metal used can also influence the maximum size of the panel. Stainless steel, for example, is available from BSC (Stainless) Sheffield in coils up to 1520 mm wide. Similarly, zero-carbon flattened steel, necessary for the manufacture of vitreous enamelled panels, is available in widths up to 1520 mm. Consequently, the size of vitreous enamelled panels is normally restricted in size to 2950 mm x 1450 mm allowing for flange dimension. Panels can of course be assembled into a larger assembly using supporting framing: for example, facade units 3.86 m wide x 4.42 m high at Burne House Telecommunications Centre,
London, were made up from panels less than I m wide mounted Into a steel channel cladding frame. The construction Incorporates a vapour barrier and a conventional Inner lining. As well as one-off designs for specific projects, a number of proprietary panel systems are marketed in the UK using box-type construction with both steel and aluminium metal skins. For details of these systems see Brookes and Stacey (1990).
Several early Russian examples of box-type composite panels and their joints are shown in Fig. 6.35. Experience in the use of composite panels in New Zealand is also reported by Sharman and Duncan (1980).
In the same way as some allowance must be made for thermal expansion using sheet metals, similarly for box-type panels consideration must be made for possible thermal movement, particularly
when using aluminium. Simple calculation shows that if the interior panel temperature varies by 20°C, then for a I 200 mm wide panel with a steel skin (coefficient of linear thermal expansion approximately 12 x I 0~6oC) the width will vary by I mm. An aluminium skin would move twice this amount. Thermal movement is normally allowed for at the joint, and if an overlap H-shaped aluminium extrusion is used, then the legs of the H-section should be long enough to accommodate this movement. It is not good practice to 'gun in' a sealant into these sections to provide a final seal, as this can be squeezed out onto the face of the panel because of thermal movement (Sharman and Duncan, I 980). Vertical movement of the panels must also be allowed for in the design of any top and bottom fixings. Allowance for movement must be made in the panel fixing (Fig. 6.36).
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