Aluminium Design and Construction John Dwight

in which t and w are in mm. These agree reasonably with the BSEN.485
requirements for t=1–30 mm and w > 1000 mm. Outside these ranges,
they overestimate the tolerance.
2.2.5 Special forms of flat product
(a) Clad sheet
Sheet material in 2xxx-series alloy, and also in the stronger type of
7xxx, can be produced in a form having improved corrosion resistance
by cladding it with a more durable layer on each surface. Such a product
is achieved by inserting plates of the cladding material top and bottom
of the slab as it enters the hot-mill. As rolling proceeds, these weld on
and are steadily reduced, along with the core, the proportion of the
total thickness being about 5% per face. For 2xxx-series sheet, the cladding
is in pure aluminium, while for the 7xxx an Al–1% Zn alloy is preferred.
(b) Treadplate
Aluminium treadplate is available with an anti-slip pattern rolled into
one surface, as in steel. It is normally supplied in the stronger type of
6xxx-series alloy in the T6-condition.
(c) Profiled sheeting
This product, which can be used for many sorts of cladding, is made by
roll-forming. An important use is for the cladding of buildings, where
a trapezoidal profile is usually specified, formed from hard-rolled sheet
in 3xxx-series alloy. Some such profiles are of ingenious ‘secret-fix’ design.
(d) Embossed sheet
This is sheet having a degree of roughening (of random pattern) rolled
into one surface. It can be used in order to reduce glare. It is also
claimed to improve the stiffness slightly. Such sheet is sometimes employed
in the manufacture of profiled sheeting.
(e) Cold-rolled sections
As in steel, it is possible to produce small sections by roll-forming from
strip. However, the technique is not generally favoured for aluminium,
because extrusion has more advantages. But it comes into its own for
very thin sections, of thickness less than the minimum extrudable, say,
1 mm and under.
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