STT113 TOWER CRANE OPERATION AND SERVICE MANUAL
11B
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1
Chapter XI Slewing ring
Periodical inspection for fastening bolt of slewing ring (type 011.40.1120)
Frequency of inspection: After the initial 100 hours’ running of the slewing ring, the
pre-tension of the bolt should be inspected. Then it should be inspected once every
500 hours running. Enough pre-tension should be maintained. At the same time, the
pre-tension of the bolt should be inspected each time when the tower crane is to be
mounted and dismounted.
Method of inspection:
Should the machine be in service, make sure that the bolts to
be checked are not exposed to a tensile strength due to load or counter weights.
Using a torque wrench and, if required, a torque multiplier, check that the tightening
torque of the bolts corresponds to the values as listed in the table 11-1-1.
Occasional replacement:
It may happen that, during an inspection, one or several
bolts show a tightening torque beyond the minimum and maximum torques as stated
in the table. In such a case, it will be necessary to replace part of or all the bolts.
Systematic replacement:
The screws and bolts used for the slewing ring assembly
must be systematically replaced every seven years or 14000 hours’ operation.
Re-tightening the bolts: No matter it is after the replacement of the bolts, or the
slewing ring is re-assembled by using new bolts, the tightening of the bolts should be
carried out continuously and symmetrically in the direction of 180
°
. Then re-tighten
them one more time to make sure all the bolts on the circle have the same pre-tension.
