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Bosch Rexroth AG
| Tightening Technology
3 608 870 A47
Nexo cordless Wi-Fi nutrunner
| 3 608 870 A47/2019-10
Settling can be avoided or decreased using the following procedures:
•
Design modification, e.g. of bearing surfaces, to prevent forces exceeding the yielding points (per-
missible surface pressing) of the materials
•
selection of suitable (strong enough) materials
•
suitable surface processing of the parts to be connected prevents settling near rough surfaces.
•
Tightening processes where settling (e.g. surface roughness area) occurs while tightening is in prog-
ress; the tightening result (tightening torque) is only determined after the settling process
5.1.2.3
Temperature influences
Due to fluctuations in temperature, the parts to be connected, as well as the bolt, can stretch or compress.
Using materials with the same coefficient of expansion prevents the clamping force from changing when
the temperature does.
5.1.2.4
Securing bolted connections
Mechanical and chemical securing devices and compounds must be considered particularly as regards
to their settling characteristics. With elastic stop nuts, friction increases during tightening due to the plas-
tic insert in the nut.
5.1.2.5
Tightening factor a
A
(taking the tightening uncertainty into account)
The mounting clamp force of a bolted connection is influenced by numerous factors:
•
The spread of the friction actually occurring under the bolt head and at the thread; only an assumed
typical value can be used for calculation
•
Differences depending on the selected tightening process, e.g. fast or slow tightening of the bolt,
torque-controlled/angle-controlled process, yield point tightening
•
Precision of the tightening system used
When designing a bolted connection, the influencing factors mentioned must be taken into account so
that in the worst case (minimum mounting clamp force F
Vmin
reached), the function of the bolted connec-
tion is maintained, and that, if maximum mounting clamp force F
Vmax
is reached, the bolt is not destroyed.
The tightening factor describes the effect of the influencing factors on the mounting clamp force exerted
by tightening. The higher the tightening factor, the larger the bolted connection (bolt diameter) must be
dimensioned.
The definition for tightening factor a
A
is:
More information on typical values for the tightening factor are described in VDI guideline 2230.
a
A
F
Vmax
F
Vmin
--------------
max mounting clamp force
min required mounting clamp force
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