Tightening Torque Inspection Prior To Operation; Tightening Torque Variation - Hitachi WH 9DM Technical Data And Service Manual

7-2. Tightening Torque Inspection Prior to Operation

As described and shown in Para. 6-3-3, the output tightening torque of which the Models WH 9DM and
WR 9DM are 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.

7-3. 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. 4 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 9DM
(kgf cm)
•
(in-lbs.)
(V)
1,600
15
(1389)
1,200
(1042)
10
800
(694)
5
400
(347)
M12 x 45 (15/32" x 1-3/4") high tension bolt
(N m)
•
(tightening time: 3 sec.)
160
120
80
When full recharged
40
0 20
Fig. 4 Number of bolts driven per charge (EB 930H battery)
When completely discharged
80
40 60
--- 19 ---
100 120 140
a
(pcs.)
160