-
WHY USE BEARINGS? Bearings are mechanical components that
support, locate, or guide a moving part in equipment. The moving
part may be a rotor in the case of rotary equipment or a cross
head-piston rod piston assembly in the case of reciprocating
equipment. The primary function is to act as intermediate component
between the moving and stationary parts and reduce friction.
-
All bearings serve the primary function of keeping a rotating
part from contacting another part which may be either rotating at a
different speed or stationary. A bearing must provide stiffness to
keep the rotor in position, and it must do so while minimizing
friction. Fluid-film bearings do this by providing a thin layer of
lubricating fluid between the rotor and journal. Rolling element
bearings do this by using a set of balls or rollers that keep rotor
and stator separated.
-
CLASSIFICATION OF BEARING {A} BASED ON THE LOAD THE BEARING
SUPPORTS :RADIAL BEARING: Load acts perpendicular to the centerline
of the shaft.THRUST BEARING: Load acts along the centerline of the
shaft.LINEAR BEARING: To support the loads in a reciprocating
part{B} BASED ON LUBRICATION PRINCIPLES:ANTIFRICTION BEARINGPLAIN
BEARING
-
ANTIFRICTION BEARINGS CLASSIFICATIONRADIAL TYPE BALL Deep
grooveDouble row deep grooveSelf aligningAngular contactCYLINDRICAL
ROLLERSPHERICAL ROLLERTAPER ROLLERTHRUST BallCylindrical
RollerSpherical Roller
-
BASIC COMPONENTS OF ROLLING BEARINGS
-
PARTS OF AN ANTIFRICTION BEARINGINNER RACEOUTER RACEROLLING
ELEMENT (SPHERICAL BALL, CYLINDRICAL ROLLER, ETC)CAGE OR
SEPARATORSHIELD
-
THE MAIN FUNCTIONS OF THE CAGE ARE:Keeps the rolling elements
apart to prevent mutual contact.Keeps the rolling elements evenly
spaced to ensure a more even load distribution.Guides the rolling
elements in the unload bearing zone.Prevents the rolling elements
from falling out of separable and slew able bearings, thereby
facilitating bearing mounting.
THE MAIN FUNCTIONS OF SHIELD:It is fixed in the outer race and
has close running clearance with the inner race. It protects the
bearing from contaminating particles by preventing its entry into
the bearing. The shield may be provided in one or both sides of the
bearing.
-
DEEP GROOVE BALL BEARING Can take large radial loads and because
of deep groove can take some thrust load also. Suitable for high
speeds applicationThere are two rows of balls and hence the radial
and thrust load capacities are almost doubled.DOUBLE ROW DEEP
GROOVE BALL BEARING
-
SELF-ALIGNING BALL BEARING The inner side of the outer race has
a spherical face. Because of this bearing can take misalignment
with the shaft up to 2o ANGULAR CONTACT BEARING They can take
radial loads and large thrust loads in one direction
-
CYLINDRICAL ROLLER BEARING Since the contact between cylindrical
rollers and races is line contact , they have greater radial load
capacity SPHERICAL ROLLER BEARING These are generally made as
double row. The inside surface of the outer race is spherical and
also the roller are spherical. Can take misalignment of the bearing
with the shaft. Have greater radial load capacity as compared with
a self-aligning ball bearing
-
NEEDLE BEARING The cylindrical rollers are large in length and
smaller in diameter. Advantage of greatest load carrying capacity
with the additional advantage of less radial space.TAPERED ROLLER
The rolling elements have the shape of truncated cones or tapered
rollers. The outer the inner race tapered rollers, cage assembly
are separate. They can take large thrust loads and radial
loads.
-
THRUST BALL BEARING Thrust bearing can take thrust load only.
The races are top and bottom races instead of inner and outer race.
The top race, bottom race and rolling elements held in cage are
separate
-
BEARING DESIGNATION The first digit (or letter) designates the
bearing type,The second digit represents the width (or height)
series. The third digit the diameter series The two last digits
indicate the bore diameter (obtained by multiplying the two last
digits by five)
-
BEARING TYPE DESIGNATION0Angular contact bearing, double
row1Self-aligning ball bearing2Spherical roller bearing and
spherical roller thrust bearings3Taper roller bearing4Deep groove
ball bearing, double row5Thrust ball bearing6Deep groove ball
bearing, single row7Angular contact ball bearing, single
row8Cylindrical roller thrust bearing
-
SUPPLEMENTARY DESIGNATION Prefixes serve to identify designs
(variants) which differ in some way from the original design or
which differ from the design, which is the current production
standard.PREFIXES:GSHousing washer of a cylindrical roller thrust
bearingK Roller and cage assembly of a cylindrical roller thrust
bearingK-Inner ring with roller and cage assembly (cone) or outer
ring(cup) of a taper roller bearing belonging to an AFBMA standard
series and generally having inch dimensionLRemovable inner or outer
ring of a separable bearing e.g. L 30207-outer ring of taper roller
bearing 30207RSeparable bearing without removable inner or outer
ringWSShaft washer of a cylindrical roller thrust bearing
-
SUPPLEMENTARY DESIGNATION SUFFIXES :-Z Shield fitted at one side
of bearing.-2Z Shield fitted at both side of bearing.-ZN Z shield
at one side of bearing and snap ring groove at the other-RS Rubber
seal of synthetic rubber at one side of bearing-LS Land riding seal
(rubber seal) at one side of the bearing-N Snap ring groove in
outside cylindrical surface of outer ringCAGE:JPressed cage of
sheet metalYPressed cage of sheet brassFMachined cage of steel or
special cast ironMMachined cage of brassPMoulded cage of glass
fiber reinforced polyamide 6.6TNMolded cage of plastic
-
FACTORS INFLUENCE THE OPERATING PERFORMANCE OF THE BEARING LOAD
- MAGNITUDE AND DIRECTION.SHAFT SPEED.BEARING SIZE.OPERATING
ENVIRONMENT: TEMPERATURE AND CONTAMINATION.LUBRICATION: TYPE AND
METHOD.SEALS: TYPE AND CONDITION.SHAFT ALIGNMENT.MOUNTING AND
DISMOUNTING TECHNIQUE.SHAFT AND HOUSING FITS
-
CAUSES OF VIBRATION /NOISE IN THE BEARING DAMAGED ROLLING
ELEMENT / RACEWAY.BROKEN CAGE.PRELOADING.LUBRICATION STARVATION/
FAILURE.EXCESSIVE CLEARANCE.OUT OF ROUNDNESS OF SHAFT
/HOUSING.EXCESSIVE DRIVE UP/ INTERFERENCE FIT.LOOSE FIT ON THE
SHAFT.LACK OF SQUARENESS OF THE SHOULDER.PRESENCE OF ABRASIVE
PARTICLES.UNBALANCE.MISALIGNMENT.EXTERNAL VIBRATION.SOFT FOOTGEAR
MESH PROBLEM
-
CAUSES OF TEMPERATURE RISE IN THE BEARING DAMAGED ROLLING
ELEMENT /RACEWAY.BROKEN CAGE.PRELOADING.LUBRICATION
STARVATION/FAILURE.EXCESSIVE LUBRICANT.EXCESSIVE DRIVE UP/
INTERFERANCE FIT. LUBRICANT CONTAMINATED WITH WATER. LOOSE FIT ON
THE SHAFT. OUT OF TOLERANCE OF SHAFT / HOUSING.PRESENCE OF ABRASIVE
PARTICLES.UNBALANCE.MISALIGNMENT.BEARING DOESNT HAVE MINIMUM
LOAD.SPEED TOO HIGH.LOAD TOO HIGH.
-
STEPS TO BE TAKEN TO INCREASE THE BEARING LIFE DON'TS:Use emery
paper on bearing seating on the shafts.Damage the shaft while
dismounting a bearing.Use mechanical force on rolling elements(
balls, rollers) while mounting/dismounting a bearing.Use lubricant
for replenishment without knowing the grade of lube already in
use.Over lubricate.Lubricate frequently.Use dry felt strips for
sealing.Use old seal when the bearing is being replaced.Deviate
from O.E.M. specification without assessment of effect.Use dirty
oil for heating bearings.Keep bearings at the bottom of the bath
while heating.Use induction heaters which doesn't have
demagnetization cycle..
-
STEPS TO BE TAKEN TO INCREASE THE BEARING LIFE DO'SIntroduce
condition monitoring and built up asset history.Carry out seal
audit and rectify faulty sealing arrangements.Carry out lubrication
audit and rectify faulty lubrication practices.Introduce alignment
and balancing program.Introduce root cause failure analysis and
corrective action practice.Introduce proper mounting and
dismounting tools and practices.Train maintenance staff.Store and
handle bearing properly.Keep lubricant containers closed and
protected from contamination. Bearing maintenance room should be
clean and protected from easy ingress of dirt.