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Why does perspex warp?

Supplier: Allplastics Engineering
30 November, 2007

Perspex™ panels can warp for a number of reasons, the most common of these are:

1. Lack of expansion allowance - Perspex™ acrylic sheet has a higher thermal expansion allowance than aluminium and hence, in a typical sign, it is important that an expansion allowance is left to allow the material to move freely. Failure to leave such expansion will lead to warping of a sign. Allplastics recommends a thermal expansion allowance of 5mm per metre of sign length.

2. Panels not being top hung - for panels above 650mm height, it is recommended that Perspex™ acrylic sheet be top hung to avoid the potential for the panel to deflect and warp under self-loading.

3. Inappropriate thickness of Perspex™ sheet used - often with larger panels (1000mm) there is a tendency to use only 5 mm thick sheet. In flat panel form, this thickness of sheet can be too thin and in a badly designed and constructed sign, then warpage can occur. Moulded Perspex™ panels offer greater strength and rigidity than flat panels.

4. Moisture Absorption - this is an unusual scenario and typically occurs in thin non-illuminated sign panels attached to a newly built building or newly rendered wall. In this case, the wall is still drying out. The water evaporates and is preferentially absorbed by one face of the Perspex™ panel. In extreme cases, this can cause warping.

5. Poor Quality Sheet - signs made from acrylic sheet supplied by competitor manufacturers may be of inferior quality to Perspex ™. Excessive internal stress and lower maximum service temperatures can lead to warping in service.

In most cases, the failure of a Perspex™ panel in service can be traced to one of the above referred problems. Perspex™ is distributed exclusively in New South Wales by Allplastics. All Perspex™ products have a 10 year guarantee against retention of colour and loss of mechanical properties. Conditions apply.