Tightening Torque Variation - Hitachi WH 9DMR Technical Data And Service Manual

8-3. Tightening Torque Variation

The tightening torque of the cordless impact driver or wrench may vary slightly in accordance with the factors
described below. Salespersons are requested to advise the customer to confirm that appropriate tightening
torque is obtained by measuring the torque with an appropriate torque wrench or torque driver at the beginning of
the tightening operations, and as necessary during the tightening operations. In addition, the torque values
shown in Para. 6-3-2 above are useful as a handy reference, and may be utilized as tentative standards.
(1) Voltage of battery
Tightening torque is affected by the voltage output of the battery. For example, the relationship between
tightening torque and the number of M12 x 45 mm (15/32" x 1-3/4") high-strength bolts tightened is shown in
Fig. 6 below. As can be seen in the graph, tightening torque decreases as the number of bolts tightened
increases. This phenomenon is caused by the decline in voltage output of the battery due to the increasing
number of bolts tightened. In particular, the tightening torque decreases rapidly just before the battery is fully
discharged (range "a" in the graph). As this phenomenon is an inherent drawback in any cordless impact
driver, salespersons are requested to ensure that the customer is fully aware of and understands this
characteristic.
Model WR 9DMR
(V)
15
10
5
(2) Effects of low ambient temperatures
The tightening torque required may be reduced at low ambient temperatures or under the influence of grease
and different torque coefficients (dependent on manufacturing and finishing processes, and specified by bolt
manufacturers).
(3) Different bolt diameter
Differences in bolt diameter will cause variation of the required levels of tightening torque. Generally speaking,
tightening torque is higher for large bolts.
(4) Different materials being tightened
When a bolt is tightened into a soft material such as aluminum, plastic, wood, etc., the tightening torque is
considerably less than when the bolt is tightened into a hard material such as steel.
M12 x 45 (15/32" x 1-3/4") High-tension bolt
.
kgf cm
.
(tightening time: 3 sec.)
N m
(in-lbs)
160
1600
(1389)
120
1200
(1042)
When fully recharged
80
800
(694)
400
40
(347)
0
20
Fig. 6 Number of bolts driven per charge (EB 930H battery)
When completely discharged
40 100
60 80
--- 21 ---
a
120 140 (pcs.)
160