Session III Bearings
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BEARINGS
Session III
Copyright 2006 LTC
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DEFINITION
Bearings are a basic machine
component developed to reducefriction between moving parts, to
support moving loads, and
maintain alignment.
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TYPES OF BEARINGS
Bearing
ShaftHousing
Ball
Raceway
Housing rings
Anti-friction bearings
Plain (Journal) bearings
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JOURNAL BEARING TYPES
Solid
Split
Half
Multi-Part
Ref: Slater Schematic Approach
Tilt Pad Radial
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Kingsbury Type Bearing
with Tilted Pivoted Shoe Construction
Hydrodynamic lubrication between collar
and pivoted shoes
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PROPERTIES OF PLAIN BEARINGS
Plain bearings carry a high radial load because of the
greater surface area
They cannot handle thrust loads
Typical clearances for a plain bearing is 0.001-0.002
inches or mm per inch or mm of shaft diameter
Thrust loading is along the shaft
Radial loading
Bearing area is d x L for full bearing
and r x L for half bearing
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PLAIN BEARING CONSTRUCTION
MATERIALS
Plain bearings are constructed of a
multi-layer metals, consisting of a
backing layer and one or more
lining materials.
Backing material, usually steel,brass, or aluminum, provides
strength to bearing.
Lining material, a single layer babbit
of either soft tin alloy or lead alloy
or multiple layers of several metals,
provides for conformity,embedability.
Single layer lining is usually for light
duty applications and multi-layer
linings are for medium to heavy
duty applicationsCopyright 2006 LTC
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JOURNAL BEARING MATERIAL Bearing materials are selected based on the following
criteria Fatigue strength
Compressive strength
Embeddability
Conformability
Compatibility
Corrosion resistance
Bearing surfaces must be composed of materialsdifferent from and softer than the mating surface toprevent welding if metal to metal contact occurs
Types of material used are Tin- base babbitt ( 84% Sn, 8% Cu, 8% Sb) Lead base babbitt ( 75% Pb, 15% Sb, 1% Sn )
Copper lead
Lead bronze
Tin bronze
Aluminum alloyCopyright 2006 LTC
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BEARING MATERIALS
Softer than shaft material
Fatigue resistant - stress w/o cracking
Embedability - absorb particles Compatibility - resist galling
Conformability - malleability to shaft & bearing
Thermal conductivity - absorb & dissipate heat
Corrosion resistance - resist acids Load capacity - withstand hydrodynamic pressure
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BEARING MATERIALS
Bronze - 80% Cu, 10% Sn, 10% Pb
More tin for heavier loads
Babbitt Tin based: 84% Sn, 8% Cu, 8% Sb
Lead base: 75% Pb, 15% Sb, 1% Sn
Do not have high load carrying capacity
Fatigue failure, pounded out
Thinner layer bonded to strong backing
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PLAIN BEARINGS OIL VISCOSITY
Speed, RPM Continuous Application
ISO VGLight load 100 PSI5000-10,000
3500-5000
2000-3500
1000-2000
500-1000
300-500
100-300
50-100
50
5-10
10-15
15-22
22-32
32-46
68-100
100-150150-220
220-320
Medium Load 100-250PSI1000-2000
500-1000
300-500
100-30050-100
50
32-46
68-100
100-150
150-220220-320
320-460
Heavy Load 250 PSI100-300
50-100
< 50
320-460
460-1000
460-1000
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APPPLICATION OF LUBRICANT IN
PLAIN BEARINGS Lubricant is applied to plain bearings through holes
and distributed by means of grooves
Chamfered oil groove prevents oil from being
scraped off and allows greater oil flow for bettercooling and distribution in load zone
The grooves must be away from the load carryingsurface for better distribution
There are applications where an oil film is neededimmediately at startup of heavy rotating machines
Lift to the shaft is provided hydrostatically by feedingoil under the bearing at a pressure which will supportthe full load at startup
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GROOVING FOR OIL
Oil supplied through the oil hole
Oil distributed by the oil groove Location dependent on
Supply system
Direction of the load
Type of load (constant or variable) Do not place in load zone
Constant load - axial groove through oil hole
Variable load - circumferential groove
Collection grooves - circumferential drain Chamfer - rounding of edges Prevents oil from being scraped off
Allows for better cooling
Greater oil flow
Better distribution to load zone
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Normal lubricant
application away
From the load zone
LUBRICANT APPLICATION OF PLAIN
BEARINGS
Ref: WillsCopyright 2006 LTC
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CONTINOUS LUBRICATION WITH
DISC AND RING OILERS
Oil is thrown on top of bearing opening
Ring should be 1.5-2.0 size of shaft and oil level should be 1/8to 3/8 inch
above inside bottom of ringIf bearing speed is too fast oil will be thrown outwards and not reach
bearing
Disc lubrication can be used if shaft diameter(inches) x rpm < 8,000
Ring lubrication can be used if shaft diameter(inches) x rpm < 6,000
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PLAIN BEARING FAILURE MODES
High heat Improper grooving
Fatigue
Vibration
Shaft deflection
Contamination
Improper fit
Misalignment
Improper lubrication
Excessive load
Fretting damage to journal
bearing subject to vibration when
stationary.
Fatigue damage to journalbearing
Cleanliness of the oil supplyis essential for satisfactoryperformance and long life !!
Ref: Schematic ApproachCopyright 2006 LTC
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PRINCIPLES OF FRICTION
Sliding Friction Rolling Friction
Ref: NTN
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ANTI-FRICTION BEARINGS
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ADVANTAGES VS. PLAIN BEARING
Considerably Lower Starting Friction
High Speed Capabilities
Can Accommodate Thrust
Easily Repaired / Replaced
Can Carry High Loads (Roller Bearings)
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BEARING LOADS
Radial Load
Perpendicular to shaft.
Axial Load
Parallel to shaft center.
Ref: NTN
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LOAD ZONES AND CONTACT
POINTS
Load Zone:
The area of the bearing
supporting the load.(Approx. 1/3)
Contact Points:
Every point or surface
where loads are supportedby the bearing.
Ref: NTN
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BEARING COMPONENTS(DEEP GROOVE BALL BEARING)
Seal Rolling Elements Inner Ring
Outer ring Cage Seal
Ref: SKF
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ROLLING ELEMENT BEARING
CLASSIFICATIONS
Ball Cylindrical
Needle
TaperedSpherical
Ref: NTN
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Deep Groove
Ball Bearings Roller Bearings+Angular
Contact
Self-Aligning Cylindrical Taper Needle Spherical
Ref :SKF
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ROLLER BEARING TYPES
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ROLLER BEARING TYPES
Ref: SKFCopyright 2006 LTC
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ROLLER BEARING ELEMENTS
Ref: SKF
Oil Hole
Oil Groove
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BASIC BEARING NUMBER
SYSTEM
6 2 03
Bearing
Series
Diameter
SeriesBore
Diameter
Ref: NTNCopyright 2006 LTC
ROLLING ELEMENT BEARING
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ROLLING ELEMENT BEARING
DIMENSIONS
Inner Diameter
Bore
Outer Diameter
Width
Radial ClearancePitch Diameter =
(d+D)
2
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ROLLING ELEMENT BEARING TYPES
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ROLLING ELEMENT BEARING TYPES
Ref: Wills
Tapered bearings normally
preloaded during
installation to remove
internal clearances
between rollers and raceway
for greater stability
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BALL BEARING TYPES
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BALL BEARING TYPES
Ref: WillsCopyright 2006 LTC
ROLLING ELEMENT BEARING TYPES
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ROLLING ELEMENT BEARING TYPES
Ref: NTNCopyright 2006 LTC
BEARING LIFE DESIGNATION
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Ball Bearings
Revolutio
ns
Total Number of Bearings
Failed
BEARING LIFE DESIGNATION
The amount of time any bearing
will perform in a specifiedoperation before failure.
L-10 Life or L-10 Rating
The number of revolutions that90% of a group of identicalbearings under identicalconditions will endure beforethe first sign of fatigue failure
occurs.L-50 rating is 5x > than L-10rating
90% of rolling element bearings fail
prematurelyCopyright 2006 LTC
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PROPERTIES OF ROLLING
ELEMENT BEARING TYPESBALL BEARING DOUBLE ROW
BALL BEARING
SPHERICAL ROLLER
BEARING
TAPERED ROLLER
BEARING
HIGH SPEEDS
LOW LOADING
LOW THRUST
PRODUCES HIGH
AXIAL MOVEMENT
GIVES LOW
FRICTION
LOW COST
It is important the correct bearing is used for the application
otherwise failure can occur
The choice of lubricant depends on the severity of the conditions
LOW SPEEDS
HIGH LOADING
HIGH THRUST
PRODUCES LOW
AXIAL MOVEMENT
GIVES HIGH
FRICTION
HIGH COST
Variations of the above bearings can be found with enhanced
properties
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VISCOSITY REQUIREMENTS FOR
ROLLING ELEMENT BEARINGS
Selection of an oils viscosity for a particular bearing
type can be calculated by knowing the bearings
speed, type, size, and operating temperature
It is important to determine the correct viscosity at
the operating temperature
The bearing speed factor (ndm) is used to calculate
the viscosity needed at the operating temperature
n= RPM
ndm= n (d+D) / 2
d = bearing bore in mm
D = bearing outside diameter in mmCopyright 2006 LTC
MINIMUM VISCOSITY REQUIREMENT
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MINIMUM VISCOSITY REQUIREMENT
FOR ROLLER BEARINGS BEARINGS
Minimum Viscosity @ Operating Temperature
Ball Bearing = 13.2 cSt (70 SUS)
Cylindrical Roller =13.2 cSt (70 SUS)
Spherical Roller = 20 cSt (100 SUS)
Spherical Roller Thrust = 33 cSt (150 SUS)
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MAXIMUM SPEED RATINGS (DN)
dN = inside dia.(mm) + outside dia(mm) X RPM2
Maximum Speed Ratings
OilLubricated Radial Ball Bearings = 500k
Oil Lubricated Cylindrical Roller Bearing = 500k Oil Lubricated Spherical Roller Bearings = 290k
Oil Lubricated Thrust Ball and Roller Bearings = 280k
Grease Lubricated Radial Ball Bearings = 340k
Grease Lubricated Cylindrical Roller Bearings = 300k
Grease Lubricated Spherical Roller Bearings = 145k
Grease Lubricated Thrust ball and Roller Bearings = 140k
Sealed for Life Ball Bearings = 108k
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K FACTOR CALCULATION
K factor calculations are used to show the relationship
between viscosity and bearing life
K = v1/v v = required viscosity of the oil
v1 = actual viscosity of oil
Example: If required viscosity at operating temperature
was 13 cSt but actual oil used had a
viscosity of 26 cSt the K factor would be
2.0
Normally the higher the K factor up to a certain point the
longer the bearing life
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VISCOSITY REQUIREMENTS
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VISCOSITY REQUIREMENTS
Copyright 2006 LTC
CALCULATION OF VISCOSITY
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CALCULATIONOF VISCOSITY
REQUIREMENTS
Ref: SKFCopyright 2006 LTC
VISCOSITY TEMPERATURE
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VISCOSITY TEMPERATURE
RELATIONSHIP
Ref: SKFCopyright 2006 LTC
VISCOSITY TEMPERATURE
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VISCOSITY TEMPERATURE
RELATIONSHIP
Ref: SKF
Ref: Wills
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BEARING LUBRICANT
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BEARING LUBRICANT
REQUIREMENTS
Bearing Type
Speed
Load
Low Medium
High
Temperature
Temperature Range
Metal/ material
Cooling requirements
Viscosity
Viscosity
Viscosity Anti-wear
Extreme Pressure
Oxidation / Thermal Stability
Viscosity Index / Pour Point
Non Aggressive Additives
Lubricant Type Grease vs. Oil
Consideration Oil Requirement
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BEARING LUBRICANT
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BEARING LUBRICANT
REQUIREMENTS
Corrosion Protection
Water Resistance / Demulsibility
Pumpability
Method of Application Foam and Air Entrainment
Maintenance Intervals
Sealing
Lubricant Consolidation
Wear prevention
Corrosion Inhibitor Additives
Demulsifiers
Viscosity / Viscosity Index
Oil or Grease and Amount Balanced Anti-foam Additives
Oil Quality
Oil / Grease Seal Compatibility
Compromise
Oil Cleanliness and Filterability
Consideration Oil Requirement
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ROLLER BEARING FAILURE
ANALYSIS
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MAJOR CAUSES OF BEARING
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MAJOR CAUSES OF BEARING
FAILURES
Defective bearing
Misalignment
Faulty mounting practices Incorrect shaft and housing fits
Inadequate lubrication
Ineffective sealing Vibration while bearing not rotating
Passage of electric current through bearing
Copyright 2006 LTC
ROLLING ELEMENT BEARING
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ROLLING ELEMENT BEARING
FAILURE MODES
Fatigue Subsurface
Surface Initiated
Wear Abrasive
Adhesive
Corrosion
Moisture
Fretting
Ref: SKFCopyright 2006 LTC
ROLLING ELEMENT BEARING
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ROLLING ELEMENT BEARING
FAILURE MODES
Electrical Erosion Excessive Voltage
Current Leakage
Plastic Deformation Overload
Debris Indentation
Handling Indentation
Fracture Forced
Fatigue
Thermal CrackingRef: SKF
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EXCESSIVE LOAD
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EXCESSIVE LOAD
Excessive loads cause premature fatigueRef: Baden
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OVERHEATING
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OVERHEATING
Overheating can be caused insufficient cooling or lubrication
when loads and speeds are excessive Ref: BadenCopyright 2006 LTC
FALSE BRINELLING
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FALSE BRINELLING
Caused by externalvibration when
bearings are not
rotating.
Ref: Baden
Ref: BadenCopyright 2006 LTC
TRUE BRINELLING
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TRUE BRINELLING
Brinelling occurs when
loads exceed the
elastic limits of the ofthe ring material and
are characterized by
indentations in the
raceway.Any static overload on
sudden impact can
cause brinelling.
Ref: Baden
Copyright 2006 LTC
FATIGUE FAILURE
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FATIGUE FAILURE
This is usually called
spalling and is fracture ofthe running surface
resulting in removal of
small discrete particles
from the balls and rings.
Ref: BadenCopyright 2006 LTC
CONTAMINATION
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CONTAMINATION
One of the leading
causes of bearingfailure which causes
raceway denting
resulting in vibration
Ref: Baden
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LUBRICANT FAILURE
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LUBRICANT FAILURE
Noticeable from
discolored ball tracksand balls and excessive
wear will follow, causing
failure.
Ref: Baden
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CORROSION
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CORROSION
Red/brown areas on
balls, raceways and
cages are symptomsof corrosion.
Ref: BadenCopyright 2006 LTC
LOOSE FITS
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LOOSE FITS
Loose fits causerelative motion between
mating parts which can
cause fretting which is
generation of fine metal
particles which oxidize
to a brown or red color
Ref: BadenCopyright 2006 LTC
TIGHT FIT
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TIGHT FIT
A heavy ball wear path in the
bottom of the raceway
indicates a tight fit
Heavy ball path
Ref: Baden
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FLUTING
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Caused by vibration or
electric current as thecurrent seeks ground
which can be caused by
static short circuit, faulty
wiring, inadequate
insulation, or loose rotor
windings.
Fluting can be prevented
by insulating bearing or
putting brushes on shaft
to ground current.
FLUTING
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FRETTING CORROSION
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FRETTING CORROSION
Fretting is a form
of wear resultingfrom small
amplitude
vibrations which
generate small
wear particles
from the rubbing
surfaces; with
ferrous metals the
wear particlesoxidize
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MISALIGNMENT
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Outer Ring Shaft Misalignment
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EFFECT OF VIBRATION ON
BEARING LIFE
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BEARING LIFE BASICS
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BEARING LIFE BASICS
Vibration along with oil analysis is used on rolling element bearingsto detect impending failure
Direct correlation between vibration level changes and bearinglongevity
Seven major factors affecting impacting rolling element bearing life Shaft rpm
Design load rating of bearing
Type of rolling element Actual load applied
Lubricant ability
Contamination level
Operating temperature
Bearing life inversely proportional to speed changesdoubling
speed reduces life 50% Increasing load results in inversely exponential reduction in life
increasing load 25% decrease life by 50%
Reliabilit Ma azine Nov/Dec 1995Copyright 2006 LTC
VIBRATION FORCES
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VIBRATION FORCES
Vibration is a dynamic response to a dynamic force
Excessive vibration leads to excessive force which dramaticallyreduces bearing life
Sources of vibration Unbalance is a primary source of machine vibration and 50% more
destructive than other bearing sources
Shaft misalignment produces both radial and axial forces
Belt / drive tension Looseness
Rotor weight
Gear reaction
Process forces
Vibration has minor impact on bearing but the forces causing the
vibration affect bearing life Reducing vibration by 25% can increase ball bearing life by 137%
Reliability Magazine Nov/Dec 1995
Copyright 2006 LTC
BEARING FAILURE SUMMARY
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BEARING FAILURE SUMMARY
Poor maintenance
Poor design
Ineffective sealing Electrical arching across bearing
Wrong bearing for application
Overload or excessive speed
Insufficient lubrication
Incorrect lubrication Oil deterioration
Temperature variation
Contamination
Incorrect assembly/ installation
Misalignment
Incorrect clearances
Improper seating
Vibration
Fatigue
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BEARING MOUNTING PROCEDURES
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BEARING MOUNTING PROCEDURES Use the highest quality bearing for the application
Handle bearings with care and keep sealed until time of theinstallation
Always follow the manufacturers recommendations when installing abearing
Work in a clean and dry environment
Never wash or wipe the bearings unless recommended by themanufacturer
Never use hard objects to pound a bearing into place
Utilize induction heaters, hydraulic presses, and hot oil baths formounting interference fit bearings
Never use an air blast to spin a bearing
Never hit or use force on the race flange
Never scratch or nick the bearing on any surface
Always use bearing pullers, heaters, arbor presses, and hydraulic oilinjection to remove bearings
Treat removed used bearings as new ones when they are to bereinstalled
Copyright 2006 LTC
TEMPERATURE MOUNTING
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TEMPERATURE MOUNTING
Good practice
Oven
Induction heater
Oil bath