Bearing Replacement - Siemens 880 Installation Operation & Maintenance

Maintenance
Sleeve Bearings
CAUTION
Maintain proper oil level.
Failure to do so may cause improper lubrication of motor
resulting in damage to the equipment.
Follow lubrication instructions carefully. Avoid adding oil
while unit is running.
Motors with sleeve bearings are shipped without oil.
A rust-inhibiting film is applied at the factory to protect
bearing and journal surfaces during shipment.
Before attempting to operate any sleeve bearing
motor, the following steps must be performed.
1. Visually inspect the bearing condition. Oil ring
inspection ports and drain openings in the
housing are normally provided for this purpose.
2. Check for any accumulation of moisture. If
oxidation is discovered, all traces of it must be
removed before motor is put in service, which will
require disassembly.
3. Flush all oil piping. Fill bearing reservoirs to
normal level. Fill to mark indicated on gauge or
to center of gauge. See the table below for
recommended grades of oil.
4. Rotate shaft several turns by hand to distribute oil
over bearing parts. Make sure oil rings rotate
freely.
Recommended Grades of Turbine Oil
Motor Speed Oil Viscosity at 100°F
3600 or 3000 RPM
1800 & slower
NOTE
The oil viscosity at operating temperature is very
important in selecting proper oil and may vary in
different climates.
It is important to maintain the correct oil level, as lack
of lubrication is often the cause of bearing failure.
Inspect oil level and oil ring operation frequently. Oil
ring operation can be observed through the sight
glass mounted at the top of the bearing capsule. Oil
rings should be perfectly round, free of burrs or rough
edges, turn at constant speed and carry a noticeable
amount of oil to the top of the journal. Failure of the
oil ring to turn freely may be caused by:
ISO
Grade
140 - 160 SSU 32
300 - 350 SSU 68
1. Ring out of round (should be round to 0.062 inch)
2. Fouling on a projection of the bearing bushing.
3. Ring not balanced (heavy side will tend to remain
down).
4. Adhesion to guide slot (trapezoidal section reduces
adhesion).
5. Oil too cold or viscous, or oil level too high.
6. Shaft not level – oil ring tends to bind.
At the first sign of oil discoloration or contamination,
replace with new oil. Rapid discoloration is caused by
bearing wear, often from vibration or thrust. Change oil
as required to keep clean.
Force Feed Lubrication
Oil is metered through an orifice in oil inlet line to allow
the proper amount of lubricating oil to enter the bearing.
Conventional oil rings are also supplied with the motor
to insure temporary bearing lubrication in the event the
force feed oil supply should fail. It is important to check
oil flow frequently.
bearing failure.
Checking Sleeve Bearing Clearance
Excessive clearance can cause rapid bearing failure,
and decreased air gap between stator and rotor at the
bottom of the motor.
clearances for the 500 and 580 frame motors are in the
range of 1.7 to 2.7 mils per inch of bearing diameter.
Diametrical sleeve bearing clearances for the 708, 788,
and 880 frames are in the range of 1.0 to 2.0 mils per
inch of bearing diameter.
An accurate check of bearing clearance is obtained with
micrometer measurements of the shaft journal and
bearing bore.

Bearing Replacement

Antifriction Bearings
For typical antifriction bearing configuration, see Figures 3
and 4.
Replacement bearings may be of a different manufacturer
but must be equal to the originals used in the motor.
When ordering bearings specify as follows:
1. The complete A.F.B.M.A. (Anti-Friction Bearing
Manufacturers' Association) bearing number from the
motor nameplate.
2. Identifying numerals and manufacturer stamped on
the bearing.
3. Bearing tolerance class, i.e. - A.B.E.C.-1 (Annular
Bearing Engineers' Committee Tolerance Class One).
4. Internal radial
(Clearance Class Three).
5. Electric motor quality.
- 21 -
Lack of lubrication may cause
Diametrical sleeve bearing
clearance, i.e. – A.F.B.M.A.-3