Tightening Torque Inspection Prior To Operation; Tightening Torque Variation - Hitachi wh 14daf2 Technical Data And Service Manual

8-2. Tightening Torque Inspection Prior to Operation

As described and shown in Para. 7-2-2, the output tightening torque of which the Model WH 14DAF2 is capable in
excess of the rated tightening torque of certain bolts and screws. Accordingly, if the tightening time is prolonged
for such bolts and screws, it could cause damage to their threads or, in the worst case, cause them to be sheared
off. (This phenomenon is common to all existing impact drivers.) Particularly when tightening M6 (1/4") or smaller
screws, tightening time must be kept extremely short: 0.5 seconds or less. The customer should be advised to
carry out several screw tightening operations and adjust the tightening time as necessary by measuring the
tightening torque with an appropriate torque wrench or driver before commencing continuous operation.

8-3. Tightening Torque Variation

The tightening torque of the cordless impact driver 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. 7-2-1 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
figure below. As can be seen in the graph, the 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.
(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
manufactures).
.
kgf cm
N
(in-lbs.)
1600
160
(1389)
16
14
1200
120
(1048)
12
10
800
8
(694)
6
400
4
(347)
2
0
Number of bolts driven per charge (When using EB 1414S battery)
M12 x 45 High-strength bolt
(tightening time 3 sec.)
.
m
When fully recharged
80
When completely
40
discharged
0 20 40 60
Fig. 6
--- 13 ---
a
80 100 120