Page 236 - ELORA-Tool_Catalogue_E95

CLICKING TORQUE WRENCHES

Why is controlled fastener tightening Screw tightening using torque and tightening
important? angle

Anyone involved in modern engineering will already In many cases, it is sufficient to tighten a bolt or
know how important controlled tightening is. To screw to a certain defined torque. To ensure the
ensure safe, dependable threaded joints, clearly application of accurate, defined tightening
defined tightening forces are essential, irrespective forces, special expanding screws are used.
of whether the forces to be applied are large or Screws of this type may only be used once. In
small (such as is the case with light-weight the first stage, they are tightened to a defined
materials with a low yield point). torque and then a specified tightening angle is
applied to tighten the screw beyond the elastic
The decision on the correct tightening force is limit of the bolt.
subject to a number of factors. These include the This enables a much more accurate tightening
fastener's thread pitch, the friction in the thread force to be achieved.
and the material under the nut or screw head.
Once all the relevant factors have been taken into In addition to an ELORA torque wrench, angle
account, this results in the required tightening force controlled tightening requires a mechanical angle
that will ensure the bolted joint will not become measuring instrument (ELORA no. 2184...).
loose even under dynamic loading. By the same
token, this tightening force must not be too high as Conformity Test and Calibration
this can also cause the bolted joint to fail.
The DIN EN ISO 6789:2017 has been divided into
What exactly is torque? 2 parts. Part 1 determines requirements for
05 construction and manufacturing, including
Torque is a physical quantity in mechanics. The contents of the declaration of conformity.
international unit of measure for moment of force, Part 2, above all, determines the requirements for
or torque, is the newton metre, Nm. traceable calibration certificates and includes a
Torque is defined as a force acting perpendicular procedure to calculate measurement
to a moment arm. uncertainties.
M = F x r The ELORA Torque Wrench Calibration
A torque wrench is constructed in such a way that Laboratory is covering both parts. Each torque
it is operated by applying force to the handle. If the wrench will be delivered with a declaration of
lever ratio is changed in any way, this will result in conformance, because for most users, this is
incorrect torque values – a key issue that is absolutely sufficient.
referred to in the documentation for all ELORA In case of not being differently mentioned within
torque wrenches. inspection equipment monitoring, the DIN EN
6789:2017 specifies a working life of 12 months
or 5000 load changes being the interval for
conformity test or calibration. The interval starts
with the first use of the torque tool.

Torque
Force

Preload

Joint Nut engaging
surface
Thread with friction

Preload

Tensile strength of the screw

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