Operational Cautions - Hitachi WR 8DH Bedienungsanleitung

Bolt
Nut
Kg-cm
1200
800
400

OPERATIONAL CAUTIONS

1. Cautions on use of the speed control switch
This switch has a built-in, electronic circuit which
steplessly 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.
2. Tightening torque
Refer to Fig. 12, 13 and 14 for the tightening torque
of bolts (according to size), under the conditions
shown in Fig. 15. 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. 16 shows an example of the
relationship between tightening torque and the
number of tightenings, for a M14 × 50 high tension
bolt. As shown, tightening torque gradually weakens
with the increase in the number of tightenings. In
particular, as the torque 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 abruptly.
If this occurs, check torque level, then recharge the
battery if necessary.
Steel plate thickness t
Fig. 15
M14 × 50 High tensile bolt (tightening time 3 sec)
When full recharged
When completely discharged
0
0 20 40
Number of tightenings (PCS)/charging
*The following bolt is used.
Ordinary bolt: Strength grade 4.8
High tensile bolt: Strength grade 12.9
(
Explanation of strength grade:
4 — Yield point of bolt: 32 kgf/mm
8 — Pulling strength of bolt: 40 kgf/mm
60 80 100 120
Fig. 16
3. Work at a tightening torque suitable for the bolt
under impact
The optimum tightening torque for nuts or bolts
differs with material and size of the nuts or bolts.
An excessively large tightening torque for a small
bolt may stretch or break the bolt. The tightening
torque increases in proportionate to the operaton
time. Use the correct operating time for the bolt.
4. 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.
5. 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 is lowered.
(2) Operating time
The tightening torque increases when the operating
time increases. But the tightening torque does not
increase above a certain value even if the tool is
driven for a long time. (See Fig. 12, 13 and 14)
2
a
English
)
2
10