Machine Elements

UoN machine elements exam

3 Types of shaft loading

Torsion, Axial and transverse

What are the 3 types of shaft misalignments ?

Axial, Parallel and Angular

What Type of Misalignment does Thermal expansion cause?

Axial

What type of coupling allows for some misalignment and also provides some damping?

Flexible couplings

Name two types of Rigid Couplings

Flange Coupling

Muff coupling

2 ways the flange coupling secure onto the shafts

Interference fit

Keyed Connection

How does the muff coupling connect onto the shafts?

Tightening the screws on it to clamp onto the shafts

What is the difference between Kinematic and resilient flexible couplings

Kinematic:

Rigid components , no shock damping

Resilient:

Flexible components, provides shock damping

3 types of kinematic flexibility couplings

Claw Coupling

Bellows Coupling

Oldham Coupling

3 types of Resilient flexibility couplings

Flexible Disk Coupling

Flexible Claw Coupling

Rubber Tyre Coupling

4 example of different elements you can put on shafts

Pulley

Gear

Flywheel

Propeller

3 types of posatie drive connections

Pin

Key

Splined shaft ( shaft with build in keys)

3 Type of pin connections

Cylindrical

Taper

Roller

4 Type of Keyed connections

Plain

Taper

Gibhead

Woodruff

3 types of friction Drive connections

Interference

Taper

Clamping

Belt drive vs chain drive ( torque and speed )

Belt drive - High speed , low torque

Chain drive - Low speed , High torque

The 3 main types of drive belts

Flat belt

Vee belt

Toothed / timing belts

Rank the belts in order of which requires the most pretention

1(most) - Flat belt

2 - Vee belt

3 - Toothed belt

Belt Vs chain drive pros and cons

What are the two types of bearings

Rolling Element bearing

Plain bearing

The 2 types of loads on bearings

Radial

Thrust

Types of Lubrication

Partial lubrication :

• Boundary - Oil or grease

• Dry - Graphite powder

Film Fluid Lubrication ( no contact between shaft and bearing ) :

• Hydrostatic

• Hydrodynamic

What’s the difference between hydrostatic and hydrodynamic lubrication ?

• Hydrostatic uses a pressurized fluid to ensure no contact all the time

• Hydrodynamic requires the shaft to rotate at high ish speeds for no contact

Which is typically made out of a harder mateiral, bearings or shaft?

Shafts , typically made from hardened steel

What should the ratio of bearing length to diamiter be

Length should be 1 to 1.5 x the diameter

L = 1.5D

What is the PV value of a bearing and what ‘safety factor’ should be included when choosing a bearing with a PV value

PV value = the pressure x velocity the shaft will experience

Safety factor of x2. E.g. use a bearing of PV value 2x what it requires

Selecting bearing from PV chart

For a rolling element bearing ( like a ball bearing ) are the contact stresses high or low?

High as force is through a small area

Single row deep groove ball bearing can it take:

• Radial Loads?

• Axial/thrust Loads?

• Misalignment ?

Takes Radical loads

Can take some small Axial loads

Cannot take misalignment - will seize up

What type of cylindrical rollers are there for bearings?

Cylindrical roller

Taper roller

Needle roller

Spherical roller ( symmetrical and asymmetrical)

Cylindrical roller bearing ( basic type ) can it take:

• High or low radial loads?

• Thrust loads?

Can take high radial loads

Cannot take thrust loads

Needle roller bearings radial and thrust load capacity

Can take radial loads

Low thrust load capacity

Taper roller bearing radial and thrust load capacity

Good Radical load capacity

Can withstand thrust loads in one direction

What type of rolling element bearing can only withstand thrust loads?

Thrust roller bearing

Bearing life- what do these mean:

• Basic static load rating

• Basic dynamic load rating

• Rated life

• Basic static load rating - Maximum radial load of non rotating bearing

• Basic dynamic load rating (C) - constant radial load (P) which it can withstand for 1 million revolutions

• Rated life - number of revolutions bearing expected to last

L10 = number of revolutions

Plain vs rolling element bearing