Technical information

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Sheet metal
Sheet metal, in various quali-
ties, hardness’s, thickness’s and
surface treatments, is widely
used in light fittings. The mate-
rial provides a good balance
between function and cost.
Sheet metal has the advantage
that it can be formed quickly in
constant production, allowing
the final product to be com-
pleted at a later stage, facilitating flexible production. From the raw
material (sheet metal), it is possible to run through the processes of
punching, bending, welding and painting to final fitting instantly,
with the only restrictions being the capacity of the manufacturer.
Certain parts may require the use of so-called deep drawing qual-
ity (soft sheet) metal, i.e. sheet metal stretched so intensely that
ordinary sheet metal qualities would break.
Black sheet
Black sheet, also referred to as iron plate, is an untreated sheet
metal that is extremely prone to rusting, at dierent rates depend-
ing on the composition of the external environment. To avoid corro-
sion, the sheet plate is surface treated (powder coated, for example),
usually using an epoxy-polyester mixture. The coating process is
free of aromatic solvents and heavy metals.
This quality is most frequently used for light fittings designed for
use in a dry environment such as oces, corridors, classrooms, etc.
Aluminium-zinc coated sheet metal
Coating sheet metal with aluminium-zinc is a very eective way
of preventing corrosion. Aluzink® coated sheets are made in the
same way as hot-dip galvanised sheet metal, but use a mixture of
approximately 55 % aluminium and 43 % zinc, rather than just zinc,
to coat the surface. Parts made of Aluzink® are immediately ready
for use following shaping, welding and bending. It is therefore cost-
eective as, in some cases, the need for lacquering can be avoided.
When welding and cutting, the cut surfaces self-seal to restore rust
protection.
The moiré eect of Aluzink® gives it an aesthetically pleasing ef-
fect. The sheet is normally used in industrial luminaires as a casing
or end piece. Other applications include brackets and other sheet
metal parts that are not normally visible but which require protec-
tion against rust.
White rust can occur in some humid or otherwise extreme envi-
ronments. Aluzink® is a registered trademark of SSAB.
Properties of materials
Stainless steel
Stainless (rustless) steel is, as the name suggests, steel that cannot
rust. This, however, is a fact that requires qualifying, as stain-
less steel can rust even though its resistance to corrosion is good.
Perhaps, instead, it should be called rust-resistant steel. In order to
retain the rust protection of steel, acid must be allowed to come
into contact with the surface. This makes it important to keep the
surface of the sheet properly cleaned.
The steel gains its properties through various alloys, including
chrome, nickel and molybdenum. Depending on its composition, it
is possible to have magnetic steel that can be hardened or non-
magnetic steel that cannot be hardened. Its non-rusting qualities
are very well suited for use in springs and Fagerhult also makes
casings and brackets in stainless steel where suitable.
Acid-proof stainless steel
Acid-proof stainless steel has even greater resistance to corrosion
than stainless steel. The steel gains its properties through various
alloys, including chrome, nickel, manganese, titanium, niobium and
molybdenum.
This is the highest level of protection oered by Fagerhult and is
normally associated with luminaires designed for external environ-
ments, such as industrial activities which handle acids, salts and
other corrosive substances. An installation that is close to the coast
can also put a strain on normal lighting fittings. Acid-proof stainless
steel can still corrode if the surface becomes coated in dirt and acid
is not able to penetrate down to the surface of the material.
Usually, acid-proof stainless steel is combined with other equally
hardy materials such as glass rather than plastic so as to ensure the
best possible encapsulation.
Aluminium with good light-reflecting properties
For good light-reflecting properties, it is important to use extremely
clean materials. Allowing the degree of cleanliness to fall by a tenth
of a per cent can cause a significant loss in eciency. There are
compositions of sheet metal (platings) where the base material is
“impure” and is covered with a layer of pure aluminium. The surface
is then chemically anodised to make it resistant to oxidation by
contact with acid or other substances. Plated materials oer one
solution for combining good performance with low cost.
Other ways of producing eective reflective sheet surfaces (fac-
tor > 92 %) are to use a layer of oxide and to vacuum metallise the
surface. See the section on louvres and reflectors.
Various impressions can be made in the sheet surface to provide a
structure that disperses or collects the light in a deliberate way.
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