Tightening Torque Inspection Prior To Operation; Tightening Torque Variation - Hitachi WR 14VB Technical Data And Service Manual

7-2. Tightening Torque Inspection Prior to Operation

The output tightening torque of the Model WR 14VB is higher than the rated tightening torque of certain bolts.
Accordingly, if the tightening time is prolonged for such bolts, it could cause damage to their threads or, in the
worst case, cause them to be sheared off. (This phenomenon is common to all existing impact wrenches.)
The customer should be advised to carry out several bolt tightening operations and adjust the tightening time as
necessary by measuring the tightening torque before commencing continuous operation.

7-3. Tightening Torque Variation

The tightening torque of an impact wrench may vary slightly in accordance with the factors described below.
Salespersons are requested to advise the customer to confirm that appropriate tightening torque is obtained by
measuring the torque at the beginning of the tightening operations, and as necessary during tightening
operations. In addition, the torque values shown in Para. 6-2, 6-3 and 6-4 above are useful as a handy reference,
and may be utilized as tentative standards.
(1) Voltage
The tightening torque of an impact wrench is influenced by voltage. For example, the tightening torque will be
reduced to about 90% if the Model WR 14VB is operated with 90% of the rated voltage. The line voltage may
be reduced by the use of a long extension cord depending on the work sites. Take the following
countermeasures against voltage reduction caused by the resistance of an extension cord and the load
current.
Decrease the resistance of an extension cord.
Use an extension cord which is as short as possible and has a thick core.
Compensate for reduction of the voltage by using a step up transformer.
At this time, prevent the plug voltage of the main body from exceeding the rated voltage.
Advise the customer to use an extension cord which is as thick as possible (cross sectional area of the core of
the extension cord: 1.25 mm
addition, recommend the customer to use a step up transformer to step up the voltage by the amount of
reduction previously.
(2) Effects of low ambient temperatures
The tightening torque required may be reduced at low ambient temperatures or under the influence of grease
and different torque coefficients (dependent on manufacturing and finishing processes, and specified by bolt
manufacturers).
(3) Different bolt diameter
Differences in bolt diameter will cause variation of the required levels of tightening torque. Generally speaking,
higher tightening torque is required for large diameter bolts.
(4) Different materials being tightened
When a bolt is tightened into a soft material such as aluminum, plastic, wood, etc., the tightening torque is
considerably less than when the bolt is tightened into a hard material such as steel.
2 or larger) if it is unavoidable to use a long extension cord on a building site. In
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