August 2018

Fastener Tech
INSTALLATION: LET’S TALK TORQUE
In the latest instalment of his series of articles looking at the key issues concerning fixings
for roofing and cladding projects, Brian Mack, Technical Business Development Manager at
EJOT UK, looks at the installation issues concerning correct torque for self-drilling or selftapping
fasteners.
As original manufacturers, we are asked on a
daily basis about correct installation torque
for a self-drilling or self-tapping fastener –
torque being the rotational force applied to the
fastener. Sounds simple enough, but when you stop
to consider the sequence of installation stages that
one single high performance fastener is designed to
deliver, then a greater depth of understanding is
beneficial to all involved.
A self-drilling fastener installs through all of the
operational stages described above, and the
torque required is different at the drilling stage,
tapping stage, run-through and finally the
tightening stage. The component materials that
the fastener is installing and the substrate – plus
any sealants can all influence these variations of
installation torque. The dynamics and variability
– even within the same application – simply calls
for knowledge-driven control by the installer for
the fastener to then deliver the long-term
performance benefits that it was designed to do.
Setting an installation gun to a tightening torque
that may be lower than the tapping or drilling
torque is a typical example. This is especially the
case for applications such as the installation of
composite panels, where the tightening torque of
the washer against the panel face is much lower
than the generated drilling and tapping torques.
So how do we legislate for these variables and
what tools can aid correct installation?
Manufacturers’ guidance is the first port of call.
This will generally include laden speed (the speed
of the installation tool when a load is added) and
the end load, (the load placed upon the
installation tool during the installation process),
and most importantly that the fastener is
installed by depth – depth
being how far the fastener is
installed. This is usually
gauged by the compression
of the EPDM of the bonded
washer. This level of control
can be achieved initially by sight;
observing the reaction of the washer as it
seats against the installed material. Many screw
guns are, or can be, supplied with a depth
sensing nose piece. These can be set to ensure
the correct compression of the washer and
therefore the optimum clamping load of the
fastener in application.
Accurate installation
There are a wide range of electric and battery
powered tools on the market, therefore checking
the performance and speed of these is
imperative. A screwgun should be selected with a
speed suggested by the fastener manufacturer
and suitable for the drive tools – with a clutch to
disengage the drive. A tool that can be supplied
with depth sensing nose pieces that works with
the clutch will ensure fast, accurate installation.
A torque set installation tool can only be used in
applications where the repeatability of the
application is constant and where the installation
tool’s torque setting parameters are in suitable
increments. As you can imagine this is very
limited and requires in-depth torque analysis of
the application to locate the correct torque
setting.
Left: Setting the nose is achieved by
pushing the fastener into the drive
socket as far as the socket will go,
retracting it back into the body of
the screwgun. The nose-piece is
then adjusted so that the outer
edge of the washer is visible.
Impact drivers are finding their way onto
construction sites and may give the impression
that they can quickly install self-drilling and selftapping
fasteners with ease.
However, the torque generated by such
tools is at least 10x – and in some instances as
much as 100x – higher than that required to
install the fastener. In short, the installation
torques cannot be calibrated and matched to the
parameters of the fastener. This can lead to
excessive stresses within the fastener and
stripping of the fastener in the application. It can
also reduce the back-out / break-loose torque to
very low figures – reducing clamping loads and
even compromising the long-term performance of
the application. Therefore they should be avoided.
The same applies for the setting of through-bolts
and concrete anchors in general, as the
maximum torque generated by such tools can
range from 40Nm to 950Nm. These types of
anchor require a calibrated torque wrench set to
the manufacturer’s recommendations.
The message here is clear; when selecting an
installation tool, select the optimum one to suit
the installation parameters of the fastener type
specified, and carefully follow the manufacturer’s
installation instructions. Manufacturers have a
depth of knowledge – if you need advice, talk to
the technical team!
Contact EJOT UK
01977 687 040
www.ejot.co.uk
@EJOTUK_Building
62 TC AUGUST 2018