MEC302 Flashcards
Describe hydrodynamic lubrication
Lubricant is dragged into wedge between components. The lubricant pressure increase supports the applied load
What are the typical applications for hydrodynamic lubrication?
journal bearings, machine slideways, piston ring/liner.
What are the typical film thickness and coefficient of friction for hydrodynamic lubrication?
1-100 µm
0.01-0.03
Describe boundary Lubrication
Surfaces may not be fully separated. Thin chemical layers reduce the tendency of the asperities to adhere.
What are the typical applications for boundary lubrication?
metal cutting, bearing start-up or shutdown
What are the typical film thickness and coefficient of friction for boundary lubrication?
- 001-0.05 µm
0. 1-0.3 S
Describe Hydrostatic Lubrication
Lubricant pumped into the interface to separate surfaces doesn’t require movement
What are the typical applications for hydrostatic lubrication?
machine tool spindles
bearing start up
What are the typical film thickness and coefficient of friction for hydrostatic lubrication?
1-100 µm
0.01-0.03
Describe Elastohydrodynamic
Lubrication (ehl)
As hydrodynamic, but high local pressure causes increase in viscosity and elastic deformation
What are the typical applications for Elastohydrodynamic
Lubrication?
rolling element bearings,
gears, cams and tappets
What are the typical film thickness and coefficient of friction for Elastohydrodynamic lubrication?
- 1-1.0 µm
0. 001-0.01
Describe Solid Lubrication
Low shear strength solid separates surfaces.
Shears more easily than the component materials.
What are the typical applications for solid
Lubrication?
‘dry’ bearings, vacuum,
graphite, PTFE, MoS2
What are the typical film thickness and coefficient of friction for solid lubrication?
-
>0.05-0.3
What assumptions do you make for a thick disc?
axial strain is constant with radius
εA= constant
(dεA/dr = 0)
What assumptions do you make for a thin disc?
axial stress=0
if there is no load or material to push against……..
stress = 0
What does B always equal for a solid shaft?
0
as if not there would be infinite stress at the centre of the shaft which is impossible
What are the lamé equations used for?
thick cylinders subject to internal and external pressure
Where are the maximum stresses for thick cylinders subject to internal and external pressure?
inner surface
what is the axial stress for an open-ended pipe?
0
what is the axial stress for an closed-ends pipe?
EεA+v(σr+σθ)
Describe visual and optical testing techniques
Looking for flaws/ compare to perfect component