Hitachi WH 12D Handling Instructions Manual Download

Page: 42 / 46

English

NOTE

If the nut is loose on the bolt, when the nut is
turned, the bolt may turn with it, in which case the
nut does not tighten up no matter how much you
turn it. If this happens, stop the impact wrench,
tighten the nut up just a bit, then finish tightening
it with the impact wrench.

3. Number of bolt tightenings possible

(with one charge)
Please refer to the table below for the number of
bolt tightenings possible with one charge.

As shown above, the longer tightening time is, the
fewer the number of tightenings, and the shorter
the time is, the greater the number of tightenings
possible.
These values may vary slightly, according to
surrounding temperature and battery characteristics.

OPERATIONAL CAUTIONS

1. After continuous work, allow the unit to rest

When you replace the batteries after continuously
using the unit to tighten bolts, let the unit rest for
about 15 minutes. If you continue using the unit
immediatly after replacing the batteries, the motor
and switch etc. may become very hot, and may
burn out.

2. Cautions on use of the speed control switch

This switch has a built-in, electronic circuit which
infinitely varies the rotation speed. Consequently,
when the switch trigger is pulled only slightly (low
speed rotation) and the motor is stopped while
continuously driving in screws, the components of
the electronic circuit parts may overheat and be
damaged.

3. Tightening torque

Refer to Fig. 9, 10 and 11 for the tightening torque
of bolts (according to size), under the conditions
shown in Fig. 12. Please use this example as a
general reference, as tightening torque will vary
according to tightening conditions.
Tightening torque varies, depending on the battery’s
charge level. Fig. 13 shows an example of the
relationship between tightening torque and the
number of tightenings, for a M14

50 high tensile

bolt. As shown, tightening torque gradually weakens
with the increase in the number of tightenings. In
particular, as the level decreases very close to the
complete discharge (“a” margin in graph), the unit’s
impact weakens, the number of time impacts
declines and tightening torque drops off sharply.
If this occurs, check torque level, then recharge the
battery if necessary.

4. Work at a tightening torque suitable for the bolt

under impact
The optimum tightening torque for nuts and bolts
differs with material and size of the nuts and bolts.
An excessively large tightening torque for a small
bolt may stretch or break the bolt. The tightening
torque increases proportionally to the operating
time. Use the correct operating time for the bolt.

5. Holding the tool

Hold the impact wrench firmly with both hands. In
this case hold the wrench in line with the bolt.
It is not necessary to push the wrench very hard.
Hold the wrench with a force just sufficient to
counteract the impact force.

6. Confirm the tightening torque

The following factors contribute to a reduction of
the tightening torque. So confirm the actual
tightening torque needed by screwing up some
bolts before the job with a hand torque wrench.
Factors affecting the tightening torque are as follows.

(1) Voltage

When the discharge margin is reached, voltage
decreases and tightening torque declines.

Tightening time: sec

(Steel plate thickness
t = 10 mm)

Fig. 9

Tightening time: sec

(Steel plate thickness
t = 10 mm)

Fig. 10

Tightening time: sec

(Steel plate thickness
t = 25 mm)

Fig. 11

Tightening torque