advancements in dynamic sealing technology.pdf

7/29/2019 Advancements in Dynamic Sealing Technology.pdf

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Advancements in Dynamic Sealing Technology

Mechanical SealsOil Seals Bearing I solators

David C. Rober t s, P.E.

I ndust rial Engineer

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By the end of todays discussion we will be

1. What are the 3 most common dynamic sealing

2. What is the primary theory of operation behindradial lip seal technology?

3. How have advancements in elastomer material

science improved radial lip seals?

4. What are the advantages to utilizing bearing

isolator technology?

5. What is the key limitation of both labyrinth seals &bearing isolators?

6. What is the primary application for mechanical

7. What is one of the critical factors in successfulmechanical seal applications?

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Dynamic Sealing Applications

Differ from static sealing applications in that the equipments mov ng

Static sealing applications may have fluid movement, butthe machine members do not move

The most common dynamic sealing application is a rotary

machine i.e. a shaft rotates as it is supported by bearings Reciprocating applications are less common i.e. a

hydraulic application where a shaft strokes through aho sin

Our focus today will be on rotating applications

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Dynamic Sealing ApplicationsSome dynamic sealing applications

There are many, many more !

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Dynamic Sealing ApplicationsThe basics

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What are the 3 most common dynamic

Mechanical SealsRadial Lip Seals Bearing I solators

a a p ea s a. .a. o sea s; uses ynam c ru er p to engage s a tsurface

Bearing I solat ors Hybrid labyrinth seal design, provides non-contact

Mechanical Seals Utilize hard mechanical faces (and other technologies)to provide a high pressure seal for severe sealing applications

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Radial Lip Seal Theory of Operation Hydrodynamic sealing

between shaft & seal lip Oil film (meniscus) is actual seal

Oil film reduces wear, friction,

and power consumption m epen ent on sea p

geometries & shaft surfaceconditions

en m s no presen , grea erseal wear (abrasion) occurs

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Radial Lip Seal Theory of Operation The shaft surface finish isCRI TI CAL to li seal erformance

Seal Dam Most lip seals require a 10-20 inRa shaft surface finish (some designsrequire finer surfaces)

LubricationEnvironment

Surface hardness must be no lessthan 30 Rockwell C (some designs

require harder surfaces)

Meniscus

(0.00018)

(0.0046mm)

perpendicular to the axis of shaftrotation

a

the peaks-n-valleys of the finishedsurface

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Elastomer Material Science

Commonly used lip seal materials are:Nitrile Rubber NBR acr lonitrile butadiene

Hydrogenated Nitrile (HNBR)

Silicone (VMQ)

Fluoroelastomer (FKM, commonly called Viton)

Common formulations

Easy to manufacture

Large allowable tolerance

Engineered ElastomersSpecialized formulation

More difficult to manufacture

Emphasis of performance

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Elastomer Material Science

Engineered Elastomers focus on improving

Factors include:Chemical compatibility

emperature res stance

Abrasion resistance

Retention of physical properties over time

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Improving Elastomer Abrasion Resistance

Taber Wear Test measures abrasion resistance:

A precisely measured disc is subjected to a grindingprocess for a specific number of cycles

The amount of material lost is measured and compared toother samples

The lower the taber wear number the better

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Advances in elastomer formulations have lead tosi nificant im rovements in abrasion resistance

Better abrasion resistance leads to longer seal lifeand thus longer equipment uptime (MTBF)

NBR elastomerimprovements:

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Improvements in HNBR & FKM elastomers:

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Improvements in Retention of Mechanical

Focus on retention of propertiesin service 25

Hardness Change (points)

Examines:HardnessTensile Strength -5

0

5

10

15

20

Tensile Change (%)Taber Wear Factor*

% Elongation

Wear Width

Abrasion Resistance

How well are these ro erties

-25

-20

-15

-10

maintained over time?Elongation Change (%)Wear Width (in (x100))

Volume Change (%)

Mill-Right N (48713)Nitrile (49706)

Perfection

* ASTMD4060 Taber Wear Index Factor

ASTM 903 Oil Immersion (70hrs @ 200F (93C))

KLOZURE 4-Hour Dry Run

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Bearing Isolators Non-contact seals

Tradit ional Labyrint h Seal Uses complex pathway to separate

Bearing I solator Seal Uses basic labyrinth technology

Rotor moves with shaft, while statorremains static in bore

,differential, and drain back designs tomaximize sealing effect

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Advantages of Bearing Isolator Seals

Can run on soft shaft materials

or finer Can run dry

rov e ot o retent on ancontaminant exclusion

Reduce power losses due to friction

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Bearing Isolator provide significant power

Testing conducted at Garlock shows

at start up and 285 watts in normaloperation

consume 150 watts at start up and 120watts during normal operation

service life of bearing isolators can beup to 65 times longer than that oftraditional li seals

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Advances in Bearing Isolator Technology

Bearing isolator incorporating

For use in very dirty, dustyenvironments

contamination, preventing

migration into bearing system

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Advances in Bearing Isolator Technology

Split bearing isolators

without costly equipment teardown

to repair (MTTR)

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Limitations to bearing isolator technology

Because bearing isolators are,

they are subject to a commonlimitation:

Shaft

LABYRINTH SEALS CANONLY BE USED IN NON-FLOODED APPLICATIONS

Level

Oil

Oil level must be below lowestopening in labyrinth pathway

Housing

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Limitations to bearing isolator technology

Examples of flooded applications:

Shaft

Submerged

Oil LevelShaft Garlock isOil

Level

developing aflooded isolat or

design!

Housing Housing

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Mechanical Seals

The primary applications for

stuffing boxes Often replaces compression

applications

Other applications includes, ,rotary fans, food processingequipment, and more

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Mechanical Seals

Stuffing Box ImpellerDischarge

Bearing Frame

Suction

Mechanical Seal

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Mechanical Seals

Most mechanical seal designs

faces to form a dynamic seal Faces must be lapped very

bands)

Common materials used are, ,

silicon carbide

Elastomers form internal static

Springs or metal bellows load theseal

Basic Mechanical Seal Design

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Mechanical Seals

More specialized designs use

Hardened sleeve providesrunning surface for lips

Garlock PS-II Design

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Critical factor for mechanical seal

One of the most critical factors

performance are the PROCESSCONTROLS used to regulate theseal

Various types of process controlinclude:Barrier Fluids

Buffer Fluids

Controlled Flush

Controlled Quench

Convection SystemsQuench & Drain

Stand pipes

Example of Convection System

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Review

1. What are the 3 most common dynamic sealing technologies?

Radial Lip Seals, Bearing Isolators, Mechanical Seals

. a s e pr mary eory o opera on e n ra a p sea

technology? Hydrodynamic Sealing3. How has improvement in elastomer material science improved

of physical properties

4. What are the advantages to utilizing bearing isolator technology?

Non-contact seals, dry running, reduced power consumption

5. What is the key limitation of both labyrinth seals & bearingisolators? Cannot be used under flooded conditions

6. What is the primary application for mechanical seals? Pump

stu ng oxes7. What is one of the critical factors in successful mechanical seal

applications? Process controls

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For more information...

GARLOCK SEALING TECHNOLOGIES

PALMYRA, NY 14522

Ph: 1-877-427-5625

. .

www.garlock.com

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