Introduction to Rotary Lip Seals

One of the most frequently used types of seal is the rotary lip seal, generally used for sealing lubricating oil or grease in rotary shaft applications. Lip seals appeared at beginning of the 1900s and they are still unbeaten in many rotary and reciprocating applications.

1. The slides are available at my profile page in
Introductionto Rotary Lip Seals
F. Xavier Borras
9th March 2016

2. 2
INTRODUCTION TO ROTARY LIP SEALS
SEVERAL DESIGNS: SAME WORKING PRINCIPLE

3. 3
INTRODUCTION TO ROTARY LIP SEALS
WORKING REGIME

4. 2 fluid transport mechanisms:
Pressure difference P
A-P
B
Relative speed V
HOUSING
4
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
P
A P
B
moving wall
fixed wall
V
fixed wall
fixed wall
P
A P
B
n

5. 5
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
P
A P
B
SEAL
Sealing surfaces:
a)Static:norelative motion between components
b)Dynamic: relative motion between components
2 fluid transport mechanisms:
Pressure difference P
A-P
B
Relative speed V
moving wall
fixed wall
V
fixed wall
fixed wall
P
A P
B
n

6. 6
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
SEAL
P
A P
B
Sealing surfaces:
a)Static:norelative motion between components
b)Dynamic: relative motion between components
2 fluid transport mechanisms:
Pressure difference P
A-P
B
Relative speed V
moving wall
fixed wall
V
fixed wall
fixed wall
P
A P
B
n

7. 7
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
Sealing surfaces:
a)Static:norelative motion between components
b)Dynamic: relative motion between components
2 fluid transport mechanisms:
Pressure difference P
A-P
B
Relative speed V
moving wall
fixed wall
V
fixed wall
fixed wall
P
A P
B
LOAD
SHAFT
SEAL
P
A P
B
n

8. 8
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
How much LOAD is needed?
LOAD
SHAFT
SEAL
P
A P
B
GoverningVariables:
Pressuredifference,appliedload,shaftandseal
roughness,shaftandsealmaterialproprieties,
fluidproprieties,temperature.
n
no contact
contact

9. 9
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
P
A P
B
CONTACT PRESSURE =
PRESSURE DIFFERENCE
The pressure difference is used to keep the
contact tight.
n

10. 10
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
P
A P
B
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. 11
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
P
A P
B
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. 12
INTRODUCTION TO ROTARY LIP SEALS
SEALING 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
P
A P
B
n

13. 13
INTRODUCTION TO ROTARY LIP SEALS
SEALING 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
P
A P
B
n
Finite Elements Models

14. 14
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
Contact Pressure at a Microscale Level
SEAL
SHAFT LINER
LOAD
Soft rubber materials are able
to slide into the metallic
substrate

15. 15
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
Stribeck curve
Rules the Lubrication Regimes
in lubricated sliding contacts
����????????????�
??????�������
=�
??????��������??????������??????�
??????��??????��??????��??????�
??????����??????��??????��??????�
Minimum
Friction and
Wear!

16. p
hydrodynamic= 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 SEALS
SEALING PRINCIPLE
(possible cavitation)
p
hydrodynamic
CONVERGENT DIVERGENT
p
A p
B
U
??????
????????????
??????ℎ
3
12??????
??????�
????????????
=
??????
2
??????
????????????
(??????ℎ)
gap height
velocity
density
viscosity
pressure

17. 17
INTRODUCTION TO ROTARY LIP SEALS
SEALING 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
P
A P
B
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

18. •Which kind of gaps are found in the lip seal’s relative speed direction?
18
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
n
b) Not perfect seal-
housing square fit
a) Shaft-seal radial
misalignment (runout)
c) Possible shaft
axial movement
SHAFT
n
SHAFT

19. •Which kind of gaps are found in the lip seal’s relative speed direction?
16/5/16 19
INTRODUCTION TO ROTARY LIP SEALS
SEALING PRINCIPLE
SHAFT
n
b) Not perfect seal-
housing square fit
a) Shaft-seal radial
misalignment (runout)
c) Possible shaft
axial movement
SHAFT
n
SHAFT

20. •Which kind of gaps are found in the lip seals in the direction of the speed?
20
INTRODUCTION TO ROTARY LIP SEALS
SEALING 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.

21. •Which kind of gaps are found in the lip seals in the direction of the speed?
21
INTRODUCTION TO ROTARY LIP SEALS
SEALING 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.

22. ↑ 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 SEALS
SEALING PRINCIPLE
PV-value! WEAR is highly related to the Contact Temperature.
Heat generation ≈ Friction Force x Velocity

24. The slides are available at my profile page in
Introductionto Rotary Lip Seals
F. Xavier Borras
9th March 2016