Chap 8: Bearings Flashcards
ball bearing sealed or shielded to prevent?
ingress of foreign particles
ball bearing parts
outer race, inner race, cage (sometimes), ball (rolling element)
advantages of rolling element bearings
can run at high speeds
dont need constant lubrication
low rate of wear and tear
disadvantages of rolling element bearings
higher initial cost
more radial space required for bearing mounting
cannot be used for overloading or shock loading
noisier (esp. after wear and tear)
easily injured by FOD
deep groove ball bearing properties
very versatile, high speed, low friction, (locating bearings prevents axial movements)
good radial load
moderate axial load
all 3 directions
angular contact ball bearing properties
for heavier axial load
good radial load
good axial load (only in 1 direction)
2 directions
double row self aligning ball bearing properties
has outer raceways for allowance for misalignment
moderate radial load
low axial load
all 3 directions
thrust ball bearing properties
flat raceway:
low torque
groove raceway:
high axial load
good axial only in 1 direction
CANNOT carry radial load
roller bearing properties
greater radial load capacity than radial ball bearings
found in pumps, engines, crankshafts
very good radial load (only 1 direction)
CANNOT carry axial load
needle bearing properties
found on wings, slats, space restriction places
support high vibration loads
excellent radial load
poor axial load
1 direction
tapered roller bearings properties
found in wheels
for heavy radial and axial loading
2 direction
double row spherical roller bearings properties
spherical raceways for misalignment (up to 1.5 deg)
very good radial load
not suitable for axial load only
3 directions
how to calculate bore diameter from bearing number system
size code: bore diameter: 00 10mm 01 12mm 02 15mm 03 17mm
04 & above: multiply code by 5
e.g. (04 = 5x04 = 20mm)
(10 = 5x10 = 50mm)
how to mount bearings, axial securing of inner ring
locknut: using lock washer, locknut, adaptor sleeve (must be threaded)
retaining clip
L10 formula
L10 = [(Cr/Pr)^k] * 10^6 revolutions
L10 - bearing rated life
Cr - dynamic load rating (kN) (from catalogue)
Pr - applied equivalent bearing load (kN)
k - exponent ( k = 3 for ball bearings)
(k = 10/3 for roller bearings)
what is Cr
constant stationary radial load that a group of identical bearings can endure for a rating life of 1 million revolutions (10^6)
what is Pr
equivalent radial load from both radial and axial load
what is Co
load that will produce permanent distortion to raceway or elements
rating life (L10) in hours
L10h = (10^6 / 60*n) * (Cr/Pr)^k
n = speed of shaft (rpm)
L10 (rev) formula from hours
L10 (rev) = L10h * n * 60
Cr formula
Cr = Pr * ( L10 / 10^6)^(1/k)
life factor equation
fh = fn * (Cr/Pr)
fh - life factor
fn - speed factor
bearing clearance groups properties
group 2: C2/2 dots
smallest internal radial clearance
not suitable for high-speed ops
group normal: CN
used where 1 ring in an interference fit and no significant heat transfer
group 3: C3/3 dots
larger internal radial clearance
for high speeds and where temperature may affect internal clearance
group 4: C4/4 dots
for fairly high temperatures
group 5: C5/5 dots
heavy interference fit, high temperature
how to inspect rolling bearings
scheduled inspections are carried out on site
1) remove excess grease
2) wear and tear (check axial and radial direction) (can cause excessive vibration)
3) move mechanism slowly to ensure smooth ops.
4) rings usually are tight fit in the housing and on the shaft
5) play, loss of motion, corrosion in bearings are unacceptable
methods of removing bearings
mechanical extractors
pressurised oil
heat
how to clean bearings
1) wipe grease with lint-free cotton cloth
2) dry compressed air jet may be used to knock grease out
3) soak in white spirit to remove traces of grease or dirt
4) dry with clean, compressed air
5) lightly lubricate with oil
why is lubrication needed for bearings?
lubricating area of contacts, to protect the bearing from corrosion and dissipate heat
signs to look out for when inspecting bearings
corrosion, fracture, chipping, discolouration & wear on ball and races
how to test removed rolling bearings
bearing test machine to test for vibratory sound emission
whether if its within limits
factors causing bearing failure
improper lubrication misalignment FOD entering vibration fatigue
What to look out for for faults
worn races: excessive radial/axial clearance
worn balls/rollers: excessive radial/axial clearance, out of shape
creep: shiny marks caused by incorrect fit
worn cage: soft metal dust around bearing
overheating: bluing of elements
brinelling: indentation due to high speed under high load
false brinelling: indentation caused by vibration
corrosion: pitting/ watermark appearances
