Fig 617

To stack

Oven

Measuring and cutting device guidance on the performance criteria, leading to a more accurate specification for their use within the system market. This process relies on changes in attitudes towards technical specifications and quality control, and a requirement for design input from the manufacturers that may be beyond their present resources. Batch-produced sheet core manufacturers using platten presses (Fig. 6.18) and vacuum presses (Fig. 6.19) concentrate on wall panels only.

Large laminated panels (up to 7 m x 2.5 m) can be pressed together under heat using a platten press, on which a number of panels can be made up from trays, sheet insulation, edging pieces and backing sheets, and stacked together before pressing. The typical lamination process is where the outer aluminium sheet is brake pressed and welded into a dish. Into this is placed a honeycomb core with a further aluminium sheet forming the inner lining. The complete assembly is bonded together with a neoprene or timber edging

6.16 Batch production of foamed panels - horizontal foam

6.17 Batch production of foamed panels - vertical foaming.

and placed In a large platten press (Fig. 6.18). In this way laminated panels can be produced up to 2.5 m x 7.0 m long.

Vacuum presses (Fig. 6.19) can also be used to press laminated panels, but because the panels are pressed not more than two at a time the production may be slower; producing sandwich panels with either a mineral fibre, polyurethane or honeycomb core up to 1.6 m x 6.0 m long Is standard, and larger sizes may be possible after consultation.

Panels can also be laminated using large 'nip' rollers. Using pressing techniques it is possible, with care, to apply a finish prior to fabrication.

Curved panels can be produced, in one direction only, by cold rolling or pressing. Panels curved in three dimensions can be produced by deep-drawing techniques. Curved laminated panels (Fig. 6.20) will inevitably cost more than flat panels, as special forms are required to press the panels, which will increase their cost of production.

Panels using insulation boards have the advantage of batch production, allowing the production of a range of bespoke sizes with variable cores. The laminated cores can include bead polystyrene and extruded polystyrene, polyurethane, Rockwool Lamella and Foamglass. Bead polystyrene, often used in packaging, does not require a blowing agent, and is available in large size sheets, 1.2 m x 8 m nominally. However; it does have disadvantages: its thermal conductivity (k value 0.034-0.037 W/m K), shrinking immediately after manufacture, and its moisture-permeable open cell structure. Extruded polystyrene has a closed cell structure, is moisture resistant, and of a controlled density with a k value of 0.030-0.035 W/m K. Producers of extruded polystyrene now use HCFCs as foaming agent. These materials contain hydrogen and consequently have a much reduced ODP (ozone depletion potential). Polyurethane, which also has a closed cell structure, uses HCFCs to achieve a k value of 0.025 W/m K.

Mineral wool and honeycomb paper core, which normally contain polystyrene inserts within the core, are used for laminated panel production.The honeycomb core has the advantage that adhesive collects in the holes and offers good adherence to the panel skin. Additional acoustic performance, particularly where improved sound reduction at low frequencies is required, can be obtained by increasing the mass of the panel and laminating asbestos cement sheet and high-density mineral wool into the panel.

The integral strength of the metal and core allows the use of a thinner sheet of between 1.2 and 2.0 mm. Often the outer skin of the panel is brake pressed and shaped prior to being pressed, and the edges of the panel are reinforced with edging pieces of neoprene, or timber or even foamed glass. It is not unusual for these sandwich panels to be mounted within a steel or aluminium carrier system, using a capping piece and neoprene gasket to support the panel along its four edges.

The process of pressing these thinner sheets and bonding them to the rigid insulation usually provides a flatter panel than can be produced by rolling the sheet material.

An early use of pressed panels using 64 mm of mineral fibre insulation board sandwiched between two layers of I 6 gauge aluminium on 6 mm of asbestos sheet was at the Danish Embassy, London (architects: Arne Jacobsen Dissing andWeitling) (Fig. 6.21).

Laminated sheets can be manufactured as thin infill panelling, 6-10 mm thick, such as Alucobond, manufactured by Swiss Aluminium Ltd, which consists of two sheets of aluminium (Peralumen NS 41), each 0.5 mm thick, bonded to a low-density polyethylene core. The exceptional flatness and stiffness of these thin panels makes them ideal for use with glazing

6.18 Laminated panel production using platten presses.
6.19 Laminated panel production using vacuum presses.

Adhesives 127

6.20 Curved laminated panels.

techniques. For example, 2.4 m x 1.25 m panels at Winwick Quay factory Warrington (architects: Nicholas Grimshaw Partnership) are supported by a 150 mm x 25 mm extruded aluminium presslock system by Modern Art Glass (Fig. 6.22). For a detailed study of this construction see case study 30 in Brookes (1985).

Alucobond can be curved to a minimum radius of approximately 10 times the panel thickness; typical curves are 30-80 mm radius.

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