Bearings

Question 1

Function of a bearing

Answer 1

increase efficiency by reducing friction thus reducing energy loss
transfer loads
allow things to move radially and axially often in rapid motion
maintain relative positions of components

Question 2

Implications of friction

Answer 2

loss of source energy as heat
overheating leading to component distortion
component wear affecting life and service intervals

Question 3

Ways to reduce friction

Answer 3

introduce a thin fluid film between contact surfaces
introduce a solid with a low coefficient of friction between contact surfaces
replace sliding contact action with rolling motion

Question 4

3 main categories of oil film lubrication

Answer 4

hydrodynamic
hydrostatic
dry sump

Question 5

Describe hydrodynamic lubrication

Answer 5

At rest, there is contact between the shaft and the housing
As the shaft rotates, it drags oil around forming a wedge
The oil wedge supports the shaft

Question 6

Advantages and disadvantages of hydrodynamic lubrication

Answer 6

high efficiency for long periods
wet sump design adds weight
significant wear occurs when operated for shorts period due to contact before wedge formation

Question 7

Advantages and disadvantages of hydrostatic lubrication

Answer 7

increased weight

reduced start up wear because oil is pumped continuously

Question 8

Advantages and disadvantages of dry sump lubrication

Answer 8

reduced weight as the oil is pumped directly to the bearings

increased complexity and maintenance

Question 9

Bearings selection factors

Answer 9

performance
installation
cost - purchase, manufacture

Question 10

Performance factors

Answer 10

rotation velocity
loading type
lifespan

Question 11

Installation factors

Answer 11

space
positional accuracy
materials
vibration- damping properties
noise
ambient and running temperatures

Question 12

Bearing types

Answer 12

Plain-bushes
Rolling element- ball,roller
Air
Magnetic

Question 13

Plain bearings material characteristics

Answer 13

low coefficient of friction
embedability
good thermal conductivity
adequate strength

Question 14

Plain bearings characterisitics

Answer 14

generally small radial space
relatively low cost
quiet operation
vibration damping qualities
FOD tolerance
operation at low/medium speeds
high start up friction

Question 15

Roller element bearings material characteristics

Answer 15

high toughness

low wear

Question 16

Roller element bearings characteristics

Answer 16

low coefficient of friction
high speed/high load
high temperature operation
require considerable radial space
noise issues
expensive

Question 17

Air bearings(future)

Answer 17

low load capability
generally suited to high speed
no lubrication required
no contact-minimal wear

Question 18

Magnetic bearings

Answer 18

no lubrication/sealing/cooling
no contact
active control needed for stability
power required for active bearings
require back up bearings in the event of a power loss