Hitachi WH 14DAF2 Mode D'emploi page 10

English
If the unit is held at an angle to the screw being
tightened, the head of the screw may be damaged, or
the specified 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 differs 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
confirm 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
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 proportion 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.
kgf·cm N·m
Ordinary bolt
1000 100
800 80
600 60
400 40
200 20
0 0
0 1 2
Tightening time: sec
Bolt
Nut
9
M14 × 50 t=25mm
M12 × 45 t=25mm
M10 × 30 t=10mm
M8 × 30 t=10mm
(t: Steel plate thickness)
3
Steel plate thickness t
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. 14)
(3) Diameter of bolt
The tightening torque differs with the diameter of the
bolt as shown in Fig. 14. Generally a larger diameter
bolt requires larger tightening torque.
(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.
kgf·cm N·m
High tension bolt
1200 120
1000 100
800 80
600 60
400 40
200 20
0 0
0 1
Tightening time: sec
Fig. 14
*The following bolt is used.
Ordinary bolt: Strength grade 4.8
High tension 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
Fig. 15
M14 × 50 t=25mm
M12 × 45 t=25mm
M10 × 30 t=10mm
M8 × 30 t=10mm
(t: Steel plate thickness)
2 3
2
)
2