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

7-2. Tightening Torque Inspection Prior to Operation

As described and shown in Para. 6-2-3, the output tightening torque of which the Model WR 14DH 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 wrenches). 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 bolt tightening operations and adjust the tightening time as necessary by measuring
the tightening torque with an appropriate torque wrench before commencing continuous operation.

7-3. Tightening Torque Variation

The tightening torque of the cordless impact wrench may vary slightly in accordance with the factors described
below. Sales persons 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. 6-2-2 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 M16 x 55 mm (5/8" x 2-5/32") bolts tightened is shown in Fig. 7 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 wrench,
salespersons are requested to ensure that the customer is fully aware of and understands this characteristic.
(in-lbs.)
(1389 in-lbs.)
1200
(1042 in-lbs.)
800
(694 in-lbs.)
400
(347 in-lbs.)
M16 x 55 (5/8" x 2-5/32") F10T (tightening time: 3 seconds)
(kgf•cm) (N•m)
160
1600
120
1200
Fully charged
80
800
400
40
0 0
20
Number of bolts driven per charge (EB 14B battery)
Tightening torque
Battery voltage
Fully discharged
40
60 80
Fig. 7
--- 17 ---
(V)
α
14
12
10
8
6
4
2
0
120 (pcs.)
100