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/279
Bosch Rexroth AG
| Tightening Technology
3 608 870 A47
Nexo cordless Wi-Fi nutrunner
| 3 608 870 A47/2019-10
5.1.3 Tightening case (soft – hard)
Soft tightening case
A soft tightening case exists if a relative large angle of turn 1) is needed to reach the tightening torque. This
is always the case if elastic (or soft) materials are being tightened, e.g. split washers, elastomers, or seals.
When creating such bolted connections, the tightening system must withstand longer-lasting mechanical
loads.
Hard tightening case
A hard tightening case exists if the end torque is reached within a small angle of turn
1)
. The requirement
for a tightening system here is mainly to quickly end the tightening once the tightening torque has been
reached and to prevent the spindle from coasting (inertia). Only then the tightening process can be clas-
sified as safe.
Tightening case
determination
according to
ISO 5393
The definition of a hard or soft tightening case is set out in ISO 5393 as follows:
•
Hard tightening case:
Soft tightening case: Increase in torque from 10% to 100% of the target
torque within an angle of turn of 27 ° (or from 0% to 100% within 30 ° ).
•
Soft tightening case:
Soft tightening case: Increase in torque from 10% to 100% of the target
torque within an angle of turn of 650
°
(or from 0% to 100% within 720
°
).
Tightening case
determination
according to VDI/
VDE 2647
The definition is set out in VDI/VDE 2647 as follows:
•
Hard tightening case:
Increase in torque from 50% to 100% of the target torque within an angle of
turn of 30 ° .
•
Soft tightening case:
Increase in torque from 50% to 100% of the target torque within an angle of
turn of 360
°
.
The tightening case hardness is particularly relevant for selecting the speed in the last tightening step and
thus also for the cycle times
(page 54) .
5.1.4 Tightening processes
A bolted connection should be designed in a way that the minimum mounting clamp force reached guar-
antees the function of the bolted connection, but the maximum mounting clamp force does not destroy
the bolted connection or the bolt.
The following tightening processes are available for this:
•
Angle of turn-controlled tightening process
• Torque-controlled tightening process
• Special tightening processes, e.g. loosening/retightening sequence
For detailed information, please refer to chapter Tightening processes from page 257 .
5.2 Cycle times
The possible cycle time (effective minimum time for a tightening process) is determined by two factors:
•
Duration of the tightening steps
• Heat output from the nutrunner
1) The angle of turn considered here is the angle difference between reaching a threshold torque (10%
of the nominal torque) and reaching the tightening torque (end of tightening process).
There is no cycle time loss when the slide-in battery pack is changed during the buffer period
(see page 30) .