3 608 870 A47
Tightening Technology |
Bosch Rexroth AG
51
Nexo cordless Wi-Fi nutrunner
| 3 608 870 A47/2019-10
5.1.2
Determination of the required torque to create a bolted connection
When creating bolted connections, the mounting clamp force (clamping force) required for a secure con-
nection of the parts is usually specified. As the clamping force is difficult to measure, the tightening torque
or angle of turn is used as a parameter for the clamping force. When determining the clamp force using
the measured tightening torque, the following factors must be taken into account.
5.1.2.1
Friction when tightening
The most influential factor is the friction that results when tightening the bolted connection. This friction
mainly depends on the following conditions:
•
Machining quality of the parts to be tightened
•
Coarseness tolerances of bolt and nut
•
Material pairs of the parts and bolts to be tightened
•
Surface coating of bolts and components
•
Thread form and pitch
The friction consists of a combination of the thread friction and the underhead friction. The actual friction
itself does not make a calculation of the mounting clamp force from the tightening torque more difficult,
rather the distribution of the friction values from bolted connection to bolted connection.
5.1.2.2
Settling
Settling occurs when the connected parts and/or bolts are plastically distorted after the tightening and
the clamp force is permanently decreased.
Fig. 5–2:
Relation between clamp force and distortion of bolt and connected parts
Relations before the settling process (at the time of tightening)
Relations after the settling process
f
Distortion
F
Force
f
PM
Compression of the connected parts
f
SM
Extension of the bolt
f
Z
Amount of settling
F
M
Mounting clamp force before settling process
F
V
Mounting clamp force after settling process
F
Z
Loss of mounting clamp force due to settling process
F
V
F
M
F
f
F
Z
f
SM
f
PM
f
Z
F
F
M
F
V
F
Z
f
Z
f
f
PM
f
SM
