Chap 8: Bearings

Question 1

ball bearing sealed or shielded to prevent?

Answer 1

ingress of foreign particles

Question 2

ball bearing parts

Answer 2

outer race, inner race, cage (sometimes), ball (rolling element)

Question 3

advantages of rolling element bearings

Answer 3

can run at high speeds
dont need constant lubrication
low rate of wear and tear

Question 4

disadvantages of rolling element bearings

Answer 4

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

Question 5

deep groove ball bearing properties

Answer 5

very versatile, high speed, low friction, (locating bearings prevents axial movements)

good radial load
moderate axial load

all 3 directions

Question 6

angular contact ball bearing properties

Answer 6

for heavier axial load

good radial load
good axial load (only in 1 direction)

2 directions

Question 7

double row self aligning ball bearing properties

Answer 7

has outer raceways for allowance for misalignment

moderate radial load
low axial load

all 3 directions

Question 8

thrust ball bearing properties

Answer 8

flat raceway:
low torque

groove raceway:
high axial load

good axial only in 1 direction
CANNOT carry radial load

Question 9

roller bearing properties

Answer 9

greater radial load capacity than radial ball bearings
found in pumps, engines, crankshafts

very good radial load (only 1 direction)
CANNOT carry axial load

Question 10

needle bearing properties

Answer 10

found on wings, slats, space restriction places
support high vibration loads

excellent radial load
poor axial load

1 direction

Question 11

tapered roller bearings properties

Answer 11

found in wheels

for heavy radial and axial loading

2 direction

Question 12

double row spherical roller bearings properties

Answer 12

spherical raceways for misalignment (up to 1.5 deg)

very good radial load
not suitable for axial load only

3 directions

Question 13

how to calculate bore diameter from bearing number system

Answer 13

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)

Question 14

how to mount bearings, axial securing of inner ring

Answer 14

locknut: using lock washer, locknut, adaptor sleeve (must be threaded)

retaining clip

Question 15

L10 formula

Answer 15

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)

Question 16

what is Cr

Answer 16

constant stationary radial load that a group of identical bearings can endure for a rating life of 1 million revolutions (10^6)

Question 17

what is Pr

Answer 17

equivalent radial load from both radial and axial load

Question 18

what is Co

Answer 18

load that will produce permanent distortion to raceway or elements

Question 19

rating life (L10) in hours

Answer 19

L10h = (10^6 / 60*n) * (Cr/Pr)^k

n = speed of shaft (rpm)

Question 20

L10 (rev) formula from hours

Answer 20

L10 (rev) = L10h * n * 60

Question 21

Cr formula

Answer 21

Cr = Pr * ( L10 / 10^6)^(1/k)

Question 22

life factor equation

Answer 22

fh = fn * (Cr/Pr)

fh - life factor
fn - speed factor

Question 23

bearing clearance groups properties

Answer 23

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

Question 24

how to inspect rolling bearings

Answer 24

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

Question 25

methods of removing bearings

Answer 25

mechanical extractors
pressurised oil
heat

Question 26

how to clean bearings

Answer 26

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

Question 27

why is lubrication needed for bearings?

Answer 27

lubricating area of contacts, to protect the bearing from corrosion and dissipate heat

Question 28

signs to look out for when inspecting bearings

Answer 28

corrosion, fracture, chipping, discolouration & wear on ball and races

Question 29

how to test removed rolling bearings

Answer 29

bearing test machine to test for vibratory sound emission

whether if its within limits

Question 30

factors causing bearing failure

Answer 30

improper lubrication
misalignment
FOD entering
vibration
fatigue

Question 31

What to look out for for faults

Answer 31

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