Flameproof motors | 59
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- Start with or without load;
- Mechanic or reverse current brake;
- Accelerated rotating masses connected to the
motor shaft;
- Load due to rotation at the time of acceleration
and braking.
Because of the continuous effort of the motor at
start at intermittent rating originates more losses
which result in a higher heating, in special cases,
the possibility the winding of the stator may be
damaged with the motor at a standstill as a
consequence of the heating of the motor, is not out
of question.
10.1.3. DAMAGE TO THE BEARINGS
Damage to the bearings is the most frequent
causes of very long stops. Operations with
excessive vibration, inappropriate use, non-
alignments, unbalanced couplings, radial loads
and/or excessive axial loads are the main
responsible causes for the damage to the bearings.
10.1.4. SHAFT RUPTURE
Although traditionally the bearings are the most
fragile part and the shafts are designed with a wide
margin of security, it is not impossible at all for the
shafts to rupture due to the unceasing repetition of
flexion efforts caused by the excessive belt
tension.
The ruptures occur most of the time immediately
after the DE bearing.
As a consequence of the alternate flexion efforts
that require the shaft in motion, the ruptures get
deeper from the outside in until they culminate with
the rupture when the resistance of what’s still left of
the shaft section is no longer sufficient.
Avoid using additional millings on the shaft (holes
for fastening bolts, etc.) because this can cause
stress concentrations.
The replacement of only one or other parallel belts
of a transmission, besides representing a
damaging practice frequently causes ruptures in
shafts.
If some old belts are kept and consequently dilated
in length while the new and shorter ones rotate
further away from the bearing, this can cause
excessive stress on the shaft as result of flexion.
10.1.5. DAMAGE DUE TO BADLY ADAPTED
TRANSMISSION PARTS OR DEFECTIVE
ALIGNMENT OF THE MOTORS
Damaged bearings and ruptures on the shaft are,
most of the time, the result of pulleys, couplings or
pinions not appropriately set on the shaft.
These parts "hit" when rotating. The default can be
seen because of the bruising that appears on the
shaft. Key slots with their damaged edges due to
loose keys inserted may also be the cause of
ruptures on shafts. Badly aligned couplings cause
beatings and radial and axial trembling to the
bearings and, in a short time, lead to the
deterioration of the bearings and the widening of
the bearing support on the shield on the drive side.
In more serious cases, the shaft may rupture.