Reasons Why Corrosion Can Affect Your Window And
Door Hardware – And How To Avoid It
Corrosion. It's the enemy of metal. Rust never sleeps, and it's always looking for a
chance to take hold. Whatever material your window or door profiles are made
from, the steel hardware components are always under potential threat from
oxidisation.
But that's not really a problem nowadays, is it? Because all the modern hardware
has surface coatings that lasts for years. Plus, you can get some items in stainless
steel. So you don't need to worry about corrosion...do you?
It's more than the coating
When we get asked about corrosion resistance, people are usually talking about the
surface coating on the hardware. But that's not the only thing that can affect how
quickly it corrodes.
What about the screw fixings, and the possibility of reactions between different
metals? And how about those window frame materials that contain acids and
chemicals that can cause a reaction?
Stainless steel – austenitic and ferritic
Most of us are aware that there are two main types of stainless steel: austenitic and
ferritic. Now, we don't want to go into a science lesson here, but essentially, the
austenitic materials provide a higher level of corrosion resistance, but are more
expensive.
Ferritic stainless steels are less expensive, and also have the advantage of being
easier to machine. That last fact means many mechanical components in stainless
steel are of the ferritic type. In terms of corrosion resistance, they often don't
perform any better than a well-coated mild steel.
One way to tell the difference is to get hold of a magnet. High grade austenitic
stainless steels are usually non-magnetic. The more magnetic the material, the
lower the grade, and the less corrosion-resistant it will be.
Reactions between metals
You might not think reactions between different metals could be that much of a
problem, but the evidence we've seen shows it can have some alarming effects.
We once saw something extreme happen to a PVC window during the BS EN 1670
salt spray procedure.
The hinges were made from austenitic stainless steel. They should have breezed
through the test. However, the fabricator had used coated steel fixing screws. The
result: a reaction between the two dissimilar metals. The screws rusted very
quickly, to the point where the hinges virtually fell off when the sash was opened.
In other cases, we've witnessed tests where the surface coating on mild steel
hardware has been stripped away by a reaction with austenitic screws.
Opportunities for rust
Hardware should have a very long lifetime. It can achieve this, so long as you fit it
to specification and maintain it regularly. Of course, many installations are not
inspected periodically – and this where problems can start.
If moving parts aren't lubricated, there's more chance of the coating being scraped
away by friction. Of course, the possibility for corrosion then increases
dramatically.
This can also happen when hardware isn't adjusted properly, or if windows and
doors are not set up correctly. As well as fatigue stress on mechanical components,
there's a chance coatings could be eroded.
What about the coatings?
You may ask, what exactly are the coatings on mild steel hardware? How have they
advanced over the years?
If you were around before the turn of the millennium, you'll remember that most
Roto hardware used to be a gold colour. That started to change in the 1990s, when
it became clear the EU was going to ban the use of Chromium-6 in manufacturing.
So we developed the trademarked RotoSil coating. It's still an electro-deposited,
zinc-based coating, but silver in appearance.
Nano
Since then, we've refined it further, and the standard coating for most Roto products
is now RotoSil Nano. As the name indicates, it uses nano-technology. The particles
of the coating are so microscopically small, they form an exceptionally smooth
surface.
They have a degree of particle flow too, providing a 'self-healing' aspect. Sounds
very high tech, doesn't it? What's that all about?
To Russia, without damage
Essentially, it means the hardware is less likely to suffer scratch damage. A major
reason for the coating being developed was that we were exporting more and more
hardware from Germany into the Russian market.
On long journeys, often on uneven roads, bundles of components were getting
jostled about in the backs of trucks. The faceplates often got chipped and scratched.
RotoSil Nano reduces the chances of surface damage, as well as increasing
corrosion resistance.
All sorts of claims
Over the years, the industry has seen longer and longer guarantees offered on
hardware. All sorts of boasts have also been made about how long various products
have managed to endure in salt spray tests.
At Roto, when it comes to this area, we've stuck to two approaches. First, we offer
a ten year guarantee. We have never extended it beyond this period. Second, we
have never claimed corrosion resistance times longer than those defined by the
relevant standards.
A realistic guarantee
There are reasons for the ten year guarantee. It's realistic. It covers the period for
which we're obliged to be able to offer replacement parts. After this, we can't be
sure of being able to supply an alternative.
It's not that we're worried the hardware won't last. We know it can. We've often
heard of installations on which our components are still going strong after 30 years
or even longer. Not long ago, our German head office published a story about the main rail
station in Tehran, which has had the same Roto hardware on its iron and bronze
framed windows for over 50 years. But in all these cases, regular maintenance has
been important.
There's always a get-out clause
Still, we don't believe promoting huge guarantees as a marketing gimmick brings
any real value to the customer.
Some companies offer very long guarantees on paper, but we're not sure these are
worth any more than the paper itself. As mentioned earlier, most windows and
doors are not regularly maintained. There will almost always be a 'get-out' clause
for a supplier who doesn't want to honour a warranty.
Salt spray – how long?
Numbers of hours in salt spray tests are often quoted by sales people, but what do
they mean?
The test used across the industry is the one defined in EN 1670 for corrosion
resistance of building hardware. At the moment, the longest salt spray time covered
by the standard is 480 hours. That's for the highest grade of the test.
Too many red rust spots = failure
During this time, if too many red rust spots appear, the test is failed. The size and
distribution of the rust spots is also set out in the standard. So oxidisation is actually
permitted to begin: it's just not allowed to develop too quickly.
Sometimes, claims are made for hardware being able to last not just for 480 hours,
but for hundreds of hours beyond. At Roto, we've done the tests but have never got
into the practice of publishing results. The figures cannot be referenced to any
standard, and we don't like making performance claims that can't be backed up by
recognised documentation.
Anyway, it's very difficult to say how a number of hours in the salt spray test
translates to months or years in reality.
Obviously, you'd want hardware to last many, many times longer than 480 hours
without showing any signs of rust. But the amount of time windows and doors are
open, exposing hardware to the elements, varies hugely. Also, there are many other
environmental factors, other than airborne salt, that come into play.
Air quality can make a difference
Some environments are more corrosive than others, and there are variations even
across countries as relatively small as the UK.
The qualities of the air can make a big difference:
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Air is generally more corrosive the more moisture it contains
Warmer air is usually more corrosive than colder air
Polluted air is more corrosive than cleaner air – often significantly
Air containing salt is generally more corrosive.
Corrosion can be caused in other ways too.
Building site environments
Windows and doors destined for new building projects can be at risk from a
mixture of moisture and lime dust. In these cases, hardware should be protected as
much as possible.
Cleaning products
Sometimes, good intentions have unintended effects. The wrong kind of cleaning
materials can do a lot of damage. Many polishes, solvents and chemical cleaning
products cause reactions that strip coatings or start corrosion. We've sometimes
seen examples where this has happened. End users are often not given any
information about this.
Material-specific issues
Some frame materials, such as oak and engineered timbers, can contain acids.
Suppliers of these products generally issue their own guidelines, and it's advisable
to follow them closely. When using such materials, prior awareness and preparation
are very important, as we know from experience.
Preventative measures in Scotland
Several dozen oak windows on Edinburgh's Scottish Parliament building feature
Roto hardware. At the time, we marketed the project on the basis of the windows
being bomb-blast resistant. However, one of the biggest concerns during the
development of the specification was that tannic acid – naturally ocurring in the
oak – could cause premature corrosion to the hardware.
The profiles were coated with a special acrylic compound, designed to stop the acid
leeching out. Over ten years later, we've not heard about any rust. As mentioned
just now, hot air can speed up corrosion. So some might say that on a building full
of politicians, the hardware has been very resistant indeed.
But it could have been a very different story if these things had not been thought
about.
Ask us about corrosion prevention
Essentially then, an impressive corrosion test result is obviously very positive, but
it doesn't necessarily tell you everything.
You might be required to supply hardware destined for a location with an
aggressive environment, or you may just have some questions about what you're
currently doing, or planning to do.
Consult with our experts. They'll be able to tell you what we can and cannot claim
about corrosion resistance, and offer unbiased advice – based on real evidence and
experiences – to help you make sure your products stay rust free.
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