Aluprof, one of the largest producers of aluminium fenestration
systems in Europe, produce dies that are dedicated to each finish.
The more expensive, often hand finished dies, are kept for anodising
specifications. Another key to creating a good anodised finish is the
ability to extrude and anodise within a short space of time, thereby
reducing the opportunity for natural oxidisation beginning to occur.
Aluprof extrude profile through these higher quality dies which
offer higher quality surfaces with a significant reduction in ‘die
lines’ and ‘weld lines’. Once these profiles are etched and anodised
they offer a high quality surface which is both very hard wearing
and long lasting.
Anodising standards generally referred to include BS EN ISO
7599:2018 - ‘Anodising of aluminium and its alloys — Method for
specifying decorative and protective anodic oxidation coatings
on aluminium’ and QUALINOD, a independent association located
in Zurich. Whilst the QUALINOD specification includes a specific
anodising specification to meet an architectural standard; BS EN
ISO 7599 mainly deals with general anodising for engineering use
and is a method of specifying, not a specification in its own right.
Unless the specifier is experienced in agreeing the criterion for the
finished product under BS EN ISO 7599:2018, then the QUALINOD
specification should be used as it lays down criterion and it’s
licenced members are also inspected by an independent test house
to ensure compliance with the QUALINOD standard. The QUALINOD
standard does encompass almost all of BS EN 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.
Further information is available on the companies website at
aluprof.co.uk or direct from their UK office in Altrincham on 0161
941 4005.
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.