Hitachi Koki WH 12DM2 Bedienungsanleitung Seite 15

5. 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.
6. 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.
7. 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. 22 and 23).
(3) Diameter of bolt
The tightening torque differs with the diameter of
the bolt as shown in Fig. 22 and 23. Generally a
larger diameter bolt requires larger tightening torque.
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)
kgf·cm
1400
1200
1000
800
600
400
200
0
2 3
Tightening time: sec
(Steel plate thickness
t = 25 mm)
(4) Tightening conditions
The tightening torque differs according to the torque
ratio; class, and length of bolts even when bolts
with the same size threads are used. The tightening
torque also differs 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 socketis
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 fitting
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 insufficient 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. 25 shows an example 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
High tension
bolt
120
100
Ordinary bolt
80
60
40
20
0
0 1 2 3
Fig. 22
English
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 2
Tightening time: sec
(Steel plate thickness
t = 25 mm)
3
14