Fastening & Assembly Solutions & Technology July 2012

A new turn on an
aerospace fastener
Entente cordiale between France and
the United Kingdom still rides high
despite the current economic malaise stifling
Europe. And in this particular case
of rivet nut technology, it all stems from
the German company Böllhoff.
A new product has been developed primarily
for the aerospace industry which is
suitable for thin plates. A rivet nut provides
the depth of thread required while a
threaded insert provides the required
strength and load distribution. The new
component includes a Rivnut made by
Böllhoff in France, with a Helicoil from
Böllhoff Armstrong fitted into it. The
result is the Rivnut Aero which was
launched at this year’s Farnborough
International Air Show held earlier this
month. The product is intended for fitting
into very thin plate or non-metallic panels,
as found in Formula 1 and the
aerospace industry.
The Rivnut Aero essentially combines
the benefits of both Rivnut and HeliCoil.
The user is presented with a high resistance
self-locking insert nut which provides
a resistant thread on carbon steel
and aluminium plates. The design prevents
unscrewing and plate sliding and is
very flexible in use because of its all-inone
installation kit.
The shank is made of 316L stainless
steel, which ensures the necessary corrosion
resistance and mechanical characteristics.
The HeliCoil Screw-lock helical
thread insert prevents unscrewing and
plays its part in providing the desired connection
performance. The threads can be
silver-plated to prevent binding.
The design has some real advantages.
The Aero combines Rivnut’s advantages
of blind installation, reliable and reproducible
results and possibility of checking
the swage quality during the fitting operation
with those of the HeliCoil, wich
include efficient and durable antiunscrewing
to ISO 2320, a high wear
resistance of the thread as well
as excellent resistance to
vibrations and thermal shocks.
Thanks to HeliCoil’s characteristics,
the same insert can
be used for aeronautical (MJ)
or ISO (M) section bolts. High
resistance bolts can be used
while ensuring that the bolt
remains the weak element in
the assembly and is easier and
cheaper to replace.
No additional finishing is
required after setting the
Rivnut, even with coated or
painted components. Thus
blind rivet nuts and studs can
be fitted at any stage in the
production process, making
their use extremely versatile.
The short time it takes to set a
Rivnut means that blind rivet
nuts and studs have clear economic
advantages compared
with many other types of fasteners,
which may rely on
cumbersome presses and tools. This blind
rivet nut can be safely made and remade
without loss of performance so Rivnut is
also most suitable for fixing removable
panels for maintenance and inspection
purposes.
Böllhoff Armstrong serves three main
markets for it products and the tools to fit
them. The company concentrates on the
aerospace, automotive and general engineering
industries. The distribution route
accounts for 60% of production with 20%
exports. The rest is sold direct to manufacturers.
Materials used include 18-8 stainless,
Nimonic 90, Inconel X750, Zenon 100,
Phosphor bronze and special alloys. To
offset the galvanic effects of dissimilar
materials, components are plated with
cadmium, silver, zinc and Tiodize.
Böllhoff claims that Rivnut blind rivet
FAST JULY 2012
AEROSPACE FASTENERS
An Anglo-French collaboration has led to the development of a new aerospace fastener which
launched at this year’s Farnborough Air Show. Paul Gay looks at Rivnut Aero
nuts are the most versatile solution for
adding a load carrying thread to thinwalled
workpieces. They can be installed
into plastic or even ceramic components
and into all metals. The blind setting technique
means that rivet nuts and studs are
often the only fastener solution for hollow
sections, housings or where access is limited
to only one side of a component.
Commenting on the threaded insert
element of the Rivnut Aero, Lee
Burgoyne managing director of Böllhoff
Armstrong said: “Although it’s just like
bending wire, some material cost
£100,000/tonne. We all like to fly, so it’s
nice to know that [when we’re up there]
our components will stay on.”
The 1904 Entente Cordiale ended a
millennium of hostility between France
and the United Kingdom. Long may it
last.
BÖLLHOFF ARMSTRONG 01482 325425
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