Hitachi WR 12DM2 Handling Instructions Manual page 12

NOTE:
○ If a long striking time is used, screws will be strongly
tightened. This may cause the screw to break, or may
damage the tip of the bit.
○ If the unit is held at an angle to the screw being tightened,
the head of the screw may be damaged, or the specifi ed
torque may not be transmitted to the screw. Always keep
the unit and the screw being tightened in a straight line.
4. Use a tightening time suitable for the screw
The appropriate torque for a screw diff ers according to
the material and size of the screw, and the material being
screwed etc., so please use a tightening time suitable for
the screw. In particular, if a long tightening time is used in
the case of screws smaller than M8, there is a danger of
the screw breaking, so please confi rm the tightening time
and the tightening torque beforehand.
5. Work at a tightening torque suitable for the bolt
under impact
The optimum tightening torque for nuts or bolts diff ers
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 proportion to the operation time. Use the correct
operating time for the bolt.
6. Holding the tool
Hold the impact wrench fi rmly 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 suffi cient to counteract the
impact force.
7. Confi rm the tightening torque
The following factors contribute to a reduction of the
tightening torque. So confi rm the actual tightening torque
needed by screwing up some bolts before the job with
a hand torque wrench. Factors aff ecting the tightening
torque are as follows.
(1) Voltage
When the discharge margin is reached, voltage
decreases and tightening torque is lowered.
For WH12DM2
kgf·cm N·m
M10 × 30
1000
100
High tension bolt
800 80
600 60
400 40
Ordinary bolt
200
20
0 0
0 1
Tightening time: sec.
(Steel plate thickness
t = 10 mm)
12
kgf·cm
1400
1200
1000
800
600
400
200
0
2 3
(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. 14 and 15)
(3) Diameter of bolt
The tightening torque diff ers with the diameter of the bolt
as shown in Fig. 14 and 15. Generally a larger diameter
bolt requires larger tightening torque.
(4) Tightening conditions
The tightening torque diff ers according to the torque ratio;
class, and length of bolts even when bolts with the same
size threads are used. The tightening torque also diff ers
according to the condition of the surface of workpiece
through which the bolts are to be tightened. When the
bolt and nut turn together, torque is greatly reduced.
(5) Using optional parts (WR12DM2)
The tightening torque is reduced a little when an
extension bar, universal joint or a long socket is used.
(6) Clearance of the socket (WR12DM2)
A worn or deformed hex. or a square-holed socket will
not give an adequate tightness to the fi tting between the
nut or anvil, consequently resulting in loss of tightening
torque.
Using an improper socket which does not match to
the bolt will result in an insuffi cient tightening torque.
Matching socket and bolt sizes are shown in Table 1 and
2.
(7) Tightening torque varies, depending on the battery's
charge level. (WR12DM2)
Fig. 17 show examples of the relationship between
tightening torque and the number of tightenings, for
WR12DM2. 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.
N·m
M12 × 45
140
120
100
High tension bolt
80
60
Ordinary bolt
40
20
0
0 1 2 3
Tightening time: sec.
(Steel plate thickness
t = 25 mm)
Fig. 14
kgf·cm N·m
M14 × 50
1400
140
1200 120
High tension bolt
1000 100
800 80
Ordinary bolt
600
60
400 40
200 20
0 0
0 1
Tightening time: sec.
(Steel plate thickness
t = 25 mm)
2 3