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Structures & Frames
In practice Foamalux
and Foamalux Ultra are fixed to structures and frames made from many materials,
most commonly wood and metals. In the design of these, the differences in
thermal expansions must be accommodated, for example, when calculating sizes
for fixing holes. An
illustration of a typical calculation is given below.
Example calculation.
A Foamalux sheet is to be used to form a sign panel on the outside of a building. It is expected that the panel temperature will be as low as -12°C in winter and as high as 31°C in summer.
The panel measures 1.2m wide and 1.5m high in a workshop at a temperature of 18°C. The panel is to be hung from its top edge with a fixed point at the centre, so that thermal movement takes place from the top down and from the centre horizontally to each side.
Estimate the clearance required in retaining channels which will frame the bottom and sides of the sheet.
1. Width
Dimension change in cooling from 18°C to -12°C
Temperature change = 30°C
Initial width = 1.2m
Expansion coefficient = 0.068mm/m°C
Reduction in width = 1.2 x 30 x 0.068 = 2.45mm
Dimension change in heating from 18°C to 31°C
Temperature change = 13°C
Initial width = 1.2m
Expansion coefficient = 0.068mm/m°C
Increase in width = 1.2 x 13 x 0.068 = 1.06mm
Total width change = äw = 2.45 + 1.06 = 3.51mm,
say 4mm when rounded up to the nearest mm.
As the sheet is fixed at its centre it will move half
of this distance each side of the fixed point,
ie. 2mm clearance is required in each side channel.
2. Length
Dimension change in cooling from 18°C to -12°C
Temperature change = 30°C
Initial length = 1.5m
Expansion coefficient = 0.068mm/m°C
Reduction in length = 1.5 x 30 x 0.068 = 3.06mm
Dimension change in heating from 18°C to 31°C
Temperature change = 13°C
Initial length = 1.5m
Expansion coefficient = 0.068mm/m°C
Increase in length = 1.5 x 13 x 0.068 = 1.33mm
Total length change = äL = 3.06 + 1.33 = 4.39mm,
say 5mm when rounded up to the nearest mm.
As the sheet is fixed at the top it will move
vertically 5mm, ie. 5mm clearance is required in
bottom channel.
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Where large and relatively heavy panels are being fixed, the panels should be suspended from a row of fixings located near to the panel top, allowing it to expand down and to each side with temperature change. A large and relatively heavy panel mounted with most of its weight bearing on fixings near the bottom edge could distort at elevated temperatures.
Large panels mounted on external walls should be spaced from the wall surface using battens to maintain a ventilating air gap of about 20mm behind the panel. Direct mounting of the panels to the walls could result in distortion due to heat build up.
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