Clearview National April 2020 - Issue 221 | Page 39

AL UMINIUM
ISO 7599, but goes much further to ensure
anodising is fit for architectural use. Aluprof
are a licenced member of QUALINOD.
Anodising is also now becoming a choice
for pretreatment of aluminium prior to
powder coating. A very thin anodising of just
five microns seals the aluminium prior to
powder coating. This sealing or ‘conversion
coating’ has traditionally been completed in
chrome or chrome free coatings. The claim for
the use of ‘pre-anodising’ or ‘flash anodising’
prior to powder coating is that it avoids the
appearance of a type of corrosion known as
filiform corrosion.
Anodising plants are also very costly to
design and install, utilising high voltage
and specialist transformers to rapidly and
evenly create an anodised finish. Because of
its combined use of a finish in its own right
and as a ‘conversion coating’ prior to powder
coating, in the UK alone there has been two
new anodising plants come on-line in the last
couple of years with further plants planned.
As specifiers tend to specify shades of grey
for the majority of fenestration projects,
anodising can be specified in both bronze
finish and shades of grey. This is created by the
introduction of trace metals such as cobalt or
tin during the anodising process. Interestingly,
as the anodising is ‘clear’, the introduction of
these metals forms an optical colour, which
cannot fade over time.
As aluminium hardness will differ from
profile to profile and grades differ, for example
when using sheet aluminium in cill pressings,
it is inevitable that the anodic film will vary
in composition which will lead to a natural
variation in perceived colour. As aluminium
profile is extruded the material takes on a
‘grain’, so the same anodised profile turned
through 90º will also vary in shade. This is
a natural effect and most specifiers see this
offering a richness to the very hard wearing
finish that anodising can offer. To limit colour
variation it is normal for the supplier of the
anodising to offer upper and lower colour
limits at the time of specification.
Crucial for specifiers is the knowledge
that higher quality dies should be used for
producing profiles for anodising and this
is something that should find its way into
specification for the finish. It then becomes
crucial to ensure that the systems company
that can offer extrusions at a higher quality,
dedicated for anodising, also offer the finished
profile.
With these quality issues in mind, the
specifier will be aware of the need to choose a
quality company for the anodising process and
ensure that the aluminium is of the highest
quality with its surface free from natural
corrosion. It is normally best to specify an
aluminium systems supplier who can offer
quality anodising, otherwise issues can arise
where the systems company and anodiser
are unwilling to rectify issues with surface
finish problems. This can lead to expensive
replacements in finished projects. Unlike
powder coating, anodising can’t be repaired
on-site.
Since setting up the Aluprof Project Office
at the Business Design Centre in London
the systems company has rapidly grown their
specification influence in the UK with their
high performance architectural aluminium
systems. With overseas growth across Europe
spreading into the Middle East and firm roots
already in the East of the USA, the company is
becoming a global player in facade supply.
aluprof.co.uk
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