Fixing And Replacing Screws - Rohm Norm RN 1391 Informaciones Y Directivas Generales Para El Empleo De Instalaciones De Sujeción Accionadas Por Fuer

1.2.10

Fixing and Replacing Screws

If screws are replaced or undone, incorrect replacement or incorrect attach-
ment may lead to dangers for persons and objects. For this reason, for all
holding screws, the tightening torque recommended by the manufacturer of
the screw must be applied in accordance with the screw grade.
For cylinder head screws of the conventional sizes M4 – M24 and strength
classes 8.8, 10.9 and 12.9, the following tightening torque table applies:
Tightening torque in Nm
Strength M3
class
8.8 1,27 3,0 5,9 10,1 24,6 48
10.9 1,79 4,6 8,6 14,9 36,1 71
12.9 2,14 5,1 10 17,4 42,2 83
The table values do not apply to tightening torques expressly specified
elsewhere!
When replacing the original screws, the strength class specified by the manu-
facturer is to be observed. In the case of mounting screws for clamping
devices, clamping inserts, top jaws, rigid stops, pre-clamped covers, equal-
ising weights and comparable elements, strength class 12.9 is always to be
used.
All mounting screws which frequently have to be loosened and re-tightened
due to their designated use (e.g. for retooling work) are to be coated every
6 months with lubricant (grease paste) in the thread area and on the head
contact surface.
In unfavourable circumstances, even firmly tightened screws may become
loose due to external influences, e.g. vibrations. To prevent this, all safety-
critical screws (clamping fixture mounting screws, clamping set mounting
screws etc.) must be checked and if necessary re-tightened at regular inter-
vals. In the event of heavy mechanical loads, this may be necessary daily or
several times a week.
RN-1391
M4 M5 M6 M8
Safety Instructions and Guidelines | 1
M10 M12 M14 M16 M18 M20 M22 M24
84 133 206 295 415 567 714
123 195 302 421 592 807 1017
144 229 354 492 692 945 1190
EN
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