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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)
(3) Diameter of bolt
The tightening torque differs with the diameter of
the bolt as shown in Fig. 12, 13 and 14. Generally
a larger diameter bolt requires larger tightening
torque.
kgf
cm
N
m
M10 × 30
•
•
160
1600
140
1400
120
1200
High tension bolt
100
1000
80
800
60
600
40
400
Ordinary bolt
200
20
0
0
0
1
Tightening time: sec
(Steel plate thickness
t = 10 mm)
Fig. 12
Bolt
Nut
kgf
cm
•
1600
1400
1200
1000
800
600
400
200
0
2
3
Steel plate thickness t
Fig. 15
(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
The tightening torque is reduced a little when an
extension bar, universal joint or a long socketis
used.
(6) Clearance of the socket
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.
N
m
M12 × 45
•
160
High tension bolt
140
120
100
80
60
Ordinary bolt
40
20
0
0
1
2
3
Tightening time: sec
(Steel plate thickness
t = 25 mm)
Fig. 13
*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: 320 N/mm
8 — Pulling strength of bolt: 400 N/mm
English
kgf
cm
N
m
M14 × 50
•
•
160
1600
High tension bolt
140
1400
120
1200
100
1000
80
800
Ordinary bolt
60
600
40
400
200
20
0
0
0
1
2
Tightening time: sec
(Steel plate thickness
t = 25 mm)
Fig. 14
2
{32.6 kgf/mm
2
{40.8 kgf/mm
3
)
2
}
2
}
42
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