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The slides are available at my profile page in
Introduction to Rotary Lip Seals
F. Xavier Borras9th March 2016
2
INTRODUCTION TO ROTARY LIP SEALSSEVERAL DESIGNS: SAME WORKING PRINCIPLE
3
INTRODUCTION TO ROTARY LIP SEALSWORKING REGIME
2 fluid transport mechanisms:
Pressure difference PA-PB
Relative speed V
HOUSING
4
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
PA PB
moving wall
fixed wall
V
fixed wall
fixed wall
PA PB
n
5
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
PA PB
SEAL
Sealing surfaces:
a) Static: no relative motion between components
b) Dynamic: relative motion between components
2 fluid transport mechanisms:
Pressure difference PA-PB
Relative speed Vmoving wall
fixed wall
V
fixed wall
fixed wall
PA PB
n
6
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
SEAL
PA PB
Sealing surfaces:
a) Static: no relative motion between components
b) Dynamic: relative motion between components
2 fluid transport mechanisms:
Pressure difference PA-PB
Relative speed Vmoving wall
fixed wall
V
fixed wall
fixed wall
PA PB
n
7
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
Sealing surfaces:
a) Static: no relative motion between components
b) Dynamic: relative motion between components
2 fluid transport mechanisms:
Pressure difference PA-PB
Relative speed Vmoving wall
fixed wall
V
fixed wall
fixed wall
PA PB
LOAD
SHAFT
SEAL
PA PB
n
8
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
How much LOAD is needed?LOAD
SHAFT
SEAL
PA PB
Governing Variables:
Pressure difference, applied load, shaft and seal
roughness, shaft and seal material proprieties,
fluid proprieties, temperature.
n
no contact
contact
9
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
PA PB
CONTACT PRESSURE =PRESSURE DIFFERENCE
The pressure difference is used to keep the
contact tight.
n
10
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
PA PB
The Gartner spring increases
the contact pressure and
energizes the polymer.
The pressure difference is used to keep the
contact tight.
CONTACT PRESSURE =PRESSURE DIFFERENCE
SPRING FORCE
n
11
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
PA PB
CONTACT PRESSURE =PRESSURE DIFFERENCE
SPRING FORCE
MOUNTING FORCE
The Gartner spring increases
the contact pressure and
energizes the polymer.
The polymer is usually
reinforced to increase the
seal rigidity.
The pressure difference is used to keep the
contact tight.
n
12
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
CONTACT PRESSURE =PRESSURE DIFFERENCE
SPRING FORCE
MOUNTING FORCE
The Gartner spring increases
the contact pressure and
energizes the polymer.
The polymer is usually
reinforced to increase the
seal rigidity.
The pressure difference is used to keep the
contact tight.
SHAFT
PA PB
n
13
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
CONTACT PRESSURE =PRESSURE DIFFERENCE
SPRING FORCE
MOUNTING FORCE
The Gartner spring increases
the contact pressure and
energizes the polymer.
The polymer is usually
reinforced to increase the
seal rigidity.
The pressure difference is used to keep the
contact tight.
SHAFT
PA PB
n
Finite Elements Models
14
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
Contact Pressure at a Microscale Level
SEAL
SHAFT LINER
LOAD
Soft rubber materials are able
to slide into the metallic
substrate
15
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
Stribeck curve
Rules the Lubrication Regimes
in lubricated sliding contacts
𝐶𝑜𝑛𝑡𝑎𝑐𝑡𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒
= 𝑓
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒𝑆𝑝𝑟𝑖𝑛𝑔 𝐹𝑜𝑟𝑐𝑒
𝑀𝑜𝑢𝑛𝑡𝑖𝑛𝑔 𝐹𝑜𝑟𝑐𝑒
Minimum
Friction and
Wear!
phydrodynamic= f(gap, speed, lubricant proprieties)
Importance of the shape of the seal: Reynolds PDE
A) Convergent gap in the direction of the speed Pressure build-up
B) Divergent gap in the direction of the speed Pressure drop
16/5/16 16
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
(possible cavitation)
phydrodynamic
CONVERGENT DIVERGENT
pA pB
U
𝜕
𝜕𝑥
𝜌ℎ3
12𝜂
𝜕𝑝
𝜕𝑥=𝑈
2
𝜕
𝜕𝑥(𝜌ℎ)
gap height velocity
density
viscosity
pressure
17
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
Relative speed V
moving wall
fixed wall
V
Convergent gap in the direction of the speed Pressure build-up
Divergent gap in the direction of the speed Pressure drop
PA PB
SHAFTn
a)
b) c)
d)
• Which relative movements are found?
Mechanisms:a) Shaft angular speed
b) Shaft axial motion
c) Shaft radial motion
d) Shaft angular motion
• Which kind of gaps are found in the lip seal’s relative speed direction?
18
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
n
b) Not perfect seal-
housing square fit
a) Shaft-seal radial
misalignment (runout)
c) Possible shaft
axial movement
SHAFTn SHAFT
• Which kind of gaps are found in the lip seal’s relative speed direction?
16/5/16 19
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
SHAFT
n
b) Not perfect seal-
housing square fit
a) Shaft-seal radial
misalignment (runout)
c) Possible shaft
axial movement
SHAFTn SHAFT
• Which kind of gaps are found in the lip seals in the direction of the speed?
20
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
d) The orientation of the asperities in the contact zone
also plays an important role at the microscale level.
Representation of the fluid film transfer
under a seal lip.
Distortion of the contact band creates
asperities at an angle to the shaft axis.
• Which kind of gaps are found in the lip seals in the direction of the speed?
21
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
d) The orientation of the asperities in the contact zone
also plays an important role at the microscale level.
Representation of the fluid film transfer
under a seal lip.
Distortion of the contact band creates
asperities at an angle to the shaft axis.
↑ LOAD =
↓ LEAKAGE
↑ FRICTION
↑ WEAR
↑ HEAT GENERATION
↓ LIFESPAN
↑ SPEED =
↑ LEAKAGE
↓ FRICTION (if lubricated)
↑ WEAR
↑ HEAT GENERATION
↓ LIFESPAN
• What about FRICTION and WEAR?
22
INTRODUCTION TO ROTARY LIP SEALSSEALING PRINCIPLE
PV-value! WEAR is highly related to the Contact Temperature.
Heat generation ≈ Friction Force x Velocity
The slides are available at my profile page in
Introduction to Rotary Lip Seals
F. Xavier Borras9th March 2016