A torque wrench is used when the user
needs a nut, screw, or bolt to be tightened to a specific torque to prevent over
tightening and under tightening. The click-type torque wrenches are popular for
small application. The torque is set through a dial on the wrench. The unit
clicks when the nut is tightened at the set torque.
Hydraulic torque wrenches are used in
larger applications such as skyscrapers, bridges, mining, aviation, and much
more. Before these existed, pneumatic impact wrenches were used. They were much
heavier, louder, and not as accurate as hydraulic torque wrenches. Bolt
tensioners are also an alternative, but are not commonly used.
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| [torque wrench application image] |
Hydraulic torque wrenches can be
dangerous without proper caution. When torque is applied, the wrench pushes its
reaction arm up against the infrastructure to prevent the wrench from rotating
while it tightens. Workers unaware of this may pinch their fingers.
Not all hydraulic torque
wrenches have a
reaction arm (see below). These are meant to be used when reaction washers are
present (see below). Reaction washers are used between the nut and the
infrastructure and fit with its manufacturer’s torque wrench to provide a
stationary object that prevents the wrench from rotating. The washer design is
typically proprietary, so only a specific wrench may be used.
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| [reaction washer image] |
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| [torque wrench no arm image] |
Two common hydraulic torque wrench
designs are the square drive (seen above) and low-profile design (see below). Both
can be used with a reaction washer. The difference comes to the application. If
there is plenty of space to access the application, a square drive is most
beneficial because it can be used with cheaper drive head sizes than
low-profile design’s driver (sometimes called links or cassettes).
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[how torque wrench works]
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Drive heads are the wrench-like part
of the unit, so make sure the correct size is used for each nut being tightened
or the nut may be damaged, have inaccurate torque, or even injure the operator.
Usually, no special tools are needed to exchange drive heads.
Links or cassettes are used with low
profile torque wrenches to screw nuts down. These are more costly than square
drives; however, it is possible to substitute a new link size with an insert
(sometimes called reducers) for your current link.
When tightening an already tightened
bolt, you must loosen the bolt before proceeding due to inertia. Inertia is the
tendency of an object to resist change in motion. The bolt will require more
force to start the tightening than the actual torque currently applied to the
bolt.
Can A Torque Wrench Loosen Bolts?
It is not necessary to use a torque
wrench to loosen bolts. Bolts work as they do because the steel is trying to
compress after you have stretched the bolt by tightening. This combined with
heat cycles and debris can require more torque to remove the bolt than was used
to tighten it. Exceeding the max torque limit of your wrench can compromise its
accuracy. However, loosening bolts usually requires less torque because the
pitch of the threads on bolts acts like a wedge. This wedge is being squeezed,
and this helps the bolt be removed.
Torque Wrench Pumps
In order to use your hydraulic torque wrench, you will need to power it. First,
inspect your equipment for cracks, leaks, damage, debris, etc. Make sure to
check electrical, mechanical, pneumatic, and hydraulic components. Then,
connect your torque wrench to the pump using your hose. Choose your torque
setting (method and technique vary by manufacturer). Then, test that it is
working. When you are done tightening a nut, remember to release the pressure.
How To Calibrate Torque Wrenches
At some point, your hydraulic torque
wrench will need to be calibrated. The frequency to which you should calibrate
depends on a number of factors:
·
Desired
accuracy
o
You
may need to comply with certain industry standards
·
Usage
(frequency & improper usage)
o
You
may need to comply with certain industry standards
·
Storage
o
If
you use a torque wrench with a spring, you must lower the setting before
storage
·
Environment
o
A
wet environment may cause internal rusting
o
A
hot environment may cause a change in lubrication
