Brezk-íslenzk viðskipti - 01.05.1947, Page 25

BRETLAND OG ISLAND, Maí, 1947
ferrous materials, other than stain-
less steel, to rusting. This is due to
the protection given by a thin,
continuous and tenacious film of
aluminium-oxide which is always
present and is self-sealing.
3. Ready Formability by all the
Metal-working Processes, particu-
lar attention being drawn to the ease
with which structural and decorative
sections may be produced by the
extrusion process, which gives a
wider scope to the designer than the
use of rolled forms. The die-casting
and drop-forging processes allow
rapid production of components to
be accomplished at low cost and to a
high degree of dimensional accuracy.
4. The Modulus of Elasticity
is About One-third that of Steel
and this, although a disadvantage in
some respects, has been shown to
result in a reduction in the concen-
tration of stress at the juncture of
the dissimilar metals of composite
structures. This point is dealt with
in more detail later.
5. High Electrical and Thermal
Conductivity, making aluminium
particularly suitable for bus-bars.
6. A Particularly Pleasing Ap-
pearancefor Decorative Features.
—The surface of the metal and its
alloys may be varied by the different
methods of treatment available, such
as anodic oxidation.
RESISTANCE TO
CORROSION
The characteristics of aluminium
in respect of attack by sea-water and
marine atmosphere are those most
commonly questions, both by ship-
owners and by shipbuilders, and there
is, unfortunately, at present a serious
misconception regarding the cor-
rosion of aluminium and its alloys.
A great many laboratory investiga-
tions into the subject have been
carried out and reported, and from
incorrect inferences there has arisen
a popular belief that aluminium
alloys will not withstand normal
marine conditions.
This is by no means the case, and it
should be noted that many of the
investigations have been directed
towards specific alloys in various
conditions and environments often
far removed from normal service.
Corrosion by other re-agents likely
to be encountered in particular types
of vessels requires special study, but
again, in general, aluminium is often
superior to other more conventional
materials. A particularly interesting
example concerns the corrosion in
the tanks of oil tankers which is
apparently attributable to the alter-
nate cargoes of oil and sea-water
ballast in these tanks. An important
source of the severe corrosion of
steel is the formation of sulphuretted
hydrogen from sulphur and sulphur
compounds in the oil. It is believed
that the production of hydrogen
sulphide is accelerated by certain
bacteria inevitably present in these
tanks.this resulting in severe localised
corrosion and pitting. Aluminium
alloys are inappreciably attacked by
sulphur compounds of this type, and
it is likely that tanks for the carriage
of oil, and possibly other cargoes of a
like nature, would result in substan-
tial savings in maintenance cost, as
well as reducing the weight, which
would allow more cargo to be carried.
It has been shown already that the
corrosion of steel tanks can be
appreciably reduced by covering the
Q Another view of the Fish Room
inner surface with aluminium foil,
and it has been suggested that a full-
scale experiment might be under-
taken by the construction of at least
a bulkhead for a tank in a sea-going
tanker.
Another interesting application in
which resistance to corrosion is
important is the lining of fish-holds
and refrigerated chambers. This
development is now arousing some
interest, and it is anticipated that
such applications will prove success-
ful provided care is taken in the
design of the linings, particularly the
methods of making joints and the
means adopted to avoid electrolytic
action.
It was considered that further
improvement could be made by the
use of aluminium. The smooth, non-
absorbent surface does not harbour
bacteria and can be easily washed;
the metal does not corrode and is
non-toxic. Moreover, ice consump-
tion would be reduced through the
more efficient heat insulation offered
by aluminium.
Two different methods of con-
struction have so far been used and
both with complete success. In the
trawler Charmouth owned by the
Pair Fishing Company of Milford
Haven, Noral 57S sheet was used to
face wooden shelves and partitions
and to line the hull, and Noral 51S
extrusions were used as framework.
After a year’s service the metal
showed no sign of deterioration. In
the trawler Braeriach, owned by
J. V. Hepburn & Co. Ltd., of Aber-
deen, the same alloys were used to
face an insulating material of the
expanded rubber type. In both
cases the owners pronounced the
experiment completely satisfactory
after the first voyage and forecast
that when refitting became necessary,
aluminium fish rooms would be in-
stalled. The extent öf their en-
thusiasm can best be measured by
comparing the prices fetched when
the Braeriach landed its catch on the
same day as a trawler in which an
insulated wooden hold had recently
been installed. Both vessels had
been at sea for 20 days and had
fished the same waters, but
whereas the whole of the catch
of the former sold at 28/- a crate,
the catch of the latter fetched
only 8/- a crate. Ice consump-
tion in an insulated aluminium
lined fish room was reduced by
one half, and even on an unin-
sulated room considerable re-
duction has resulted from the
use of aluminium.
The next step in the development
of the aluminium lined fish room is
to simplify construction, and with
this end in view special extruded
sections are being designed. Cor-
rugated sections forming strong light
weight shelves and partitions will
slide into specially designed
stanchions, thus providing ease of
operation in handling, and at the
same time simplifying manufacture
and assembly of the components.
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