introduction to rotary lip seals

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


SHAFT

PA PB

SEAL

Sealing surfaces:

a) Static: no relative motion between components

b) Dynamic: relative motion between components



Relative speed Vmoving wall

fixed wall

V

fixed wall

fixed wall

PA PB

n

6


SHAFT

SEAL

PA PB

Sealing surfaces:






fixed wall

V

fixed wall

fixed wall

PA PB

n

7


Sealing surfaces:






fixed wall

V

fixed wall

fixed wall

PA PB

LOAD

SHAFT

SEAL

PA PB

n

8


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


SHAFT

PA PB

CONTACT PRESSURE =PRESSURE DIFFERENCE

The pressure difference is used to keep the

contact tight.

n

10


SHAFT

PA PB

The Gartner spring increases

the contact pressure and

energizes the polymer.


contact tight.


SPRING FORCE

n

11


SHAFT

PA PB


SPRING FORCE

MOUNTING FORCE




The polymer is usually

reinforced to increase the

seal rigidity.


contact tight.

n

12



SPRING FORCE

MOUNTING FORCE






seal rigidity.


contact tight.

SHAFT

PA PB

n

13



SPRING FORCE

MOUNTING FORCE






seal rigidity.


contact tight.

SHAFT

PA PB

n

Finite Elements Models

14


Contact Pressure at a Microscale Level

SEAL

SHAFT LINER

LOAD

Soft rubber materials are able

to slide into the metallic

substrate

15


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


(possible cavitation)

phydrodynamic

CONVERGENT DIVERGENT

pA pB

U

𝜕

𝜕𝑥

𝜌ℎ3

12𝜂

𝜕𝑝

𝜕𝑥=𝑈

2

𝜕

𝜕𝑥(𝜌ℎ)

gap height velocity

density

viscosity

pressure

17


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


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


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


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


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


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

introduction to rotary lip seals

Engineering