64
Bosch Rexroth AG
| Tightening Technology
3 608 878 300
System 350
| 3 608 878 300/2019-03
4.1.3
Torque ranges
Four different spindle sizes (=motor sizes) are available in the tightening system. A torque range of 0.6-
1000 Nm is provided by various combinations of spindle components:
In view of possible increases in torque, the working range of the tightening spindle should be less than
80 percent. This is a safety measure and increases the service life of the tightening spindle.
4.1.4
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
. 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
classified 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
.
Table 4–2: Torque ranges of tightening spindles in various sizes
Size
Torque range of tightening spindle
(depending on the output drive)
2
0,6 - 11 Nm
3
1,7 - 90 Nm
4
6 - 342 Nm
5
48 - 1000 Nm
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).
Summary of Contents for Rexroth Tightening System 350
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