Different types and thickness of sheet material and foam can be used for the insulation cores for composite panels.These are:
- mineral wool;
- honeycomb paper core;
- bead polystyrene rigid sheet;
- IB polystyrene rigid sheet;
- polyurethane foam (polyisocyanurate is a modified form of polyurethane to improve fire retar-dancy).
6.1 I Panels at Renault Centre
Polystyrene sheet, which is produced by heating up polystyrene granules and fusing them together with a combination of steam and pressing, is cheaper in material cost than polyurethane foam. However, polyurethane gives better insulation than polystyrene (25 mm thick polyurethane has the same insulation value as 40 mm thick polystyrene; see Fig. 6.1 3) and it is easier to manufacture. Most manufacturers of box-type proprietary panels prefer to use polyurethane or at least its modified version, polyisocyanurate, which is sometimes used because of its fire retardancy.
The use of any particular type or thickness of core depends upon the stiffness required of the whole panel and the requirements for thermal and acoustic performance. In general, for foamed materials, the higher the density the stifFer the panel, and the lower the density the better the insulation value. Note that modern foam production is now CFC-free as it no longer uses freon gas as a foaming agent.
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