15 Seals for Fluid Power Equipment Part Two Rotary Shaft Lip Seals

353

15

SEALS FOR FLUID POWER EQUIPMENT PART TWO ROTARY SHAFT LIP SEALS

E.D.HALLIGAN,

CEng, MIMechE, A M P R I . , T e c h n i c a l Manager (Product A p p l i c a t i o n s ) James Walker G Co.Ltd.

15.1

INTRODUCTION

For t h e purpose o f s e a l i n g l u b r i c a n t w i t h i n a b e a r i n g o r e x c l u d i n g f o r e i g n m a t t e r from b e a r i n g surfaces, t y p i c a l l y i n Fig.1,

t h e s p r i n g - l o a d e d r o t a r y s h a f t l i p s e a l , as shown

i s w i d e l y accepted.

The n a t u r e o f most designs p r e c l u d e s

t h e use o f t h i s t y p e o f seal f r o m o p e r a t i n g a t s i g n i f i c a n t p r e s s u r e s u n l e s s t h e s e a l i n g l i p i s adequately supported by a shaped p l a t e . much i n excess o f 2'.0

-

For p r e s s u r e c o n d i t i o n s

3.0 b a r , combined w i t h r o t a r y movement i t would be p r e -

f e r a b l e t o c o n s i d e r e i t h e r a compression p a c k i n g o r a r a d i a l f a c e mechanical s e a l as f i r s t c h o i c e .

Fig.1

Standard f a b r i c back s e a l w i t h r e t a i n i n g p l a t e .

3 54 DESIGN

15.2

A wide v a r i e t y o f l i p s e a l designs i s a v a i l a b l e i n terms o f o v e r a l l c o n s t r u c -

t i o n , m a t e r i a l , and l i p p r o f i l e .

Some a r e i n t e n d e d f o r f i t t i n g i n housings

which have no s e p a r a t e c o v e r - p l a t e and may be s u p p l i e d w i t h a r i g i d metal case t o which the s e a l i s bonded, t h e u n i t b e i n g a f o r c e - f i t

Fig.2

i n t h e housing,

(Fig.2).

T y p i c a l metal-encased s e a l .

Others have t h e advantage o f f l e x i b i l i t y by v i r t u e o f h a v i n g a p r o o f e d f a b r i c back ( F i g . 3 a ) w h i l s t r e q u i r i n g t h e p r o v i s i o n o f a r e t a i n i n g p l a ' t e t o n i p a x i a l l y the back o f t h e seal t o p r e v e n t leakage and o b v i a t e r o t a t i o n .

More recent dev-

elopments combine t h e m e r i t s o f f l e x i b i l i t y and s e l f - r e t e n t i o n

i n a metal-

supported a l l - r u b b e r

Fig.3a.

configuration (Fig.3b).

Standard f a b r i c back s e a l .

Fig.3b.

Moulded-in f l e x i b l e s t e e l band s e l f - r e t a i n i n g s e a l .

One o f the s e v e r a l advantages o f t h e f a b r i c back seal i s t h e f a c i l i t y w i t h which s p l i t s e a l s can be f i t t e d w i t h o u t r e d u c i n g performance which, cases,

i s o f t h e same o r d e r o f e f f i c i e n c y as an endless r i n g .

i n many

A rubber i n l a y

i s f r e q u e n t l y moulded i n t o t h e back o f such a seal t h r o u g h which the s p l i t i s effected.

The rubber abutment which r e s u l t s ensures good s e a l i n g across t h e

s p l i t portion. The p r o f i l e o f t h e l i p c o n t a c t area i s s u b j e c t e d t o each m a n u f a c t u r e r ' s design p h i l o s o p h y .

Some h a v e a knife-edge c o n t a c t band and r e l y on heavy as-

355 moulded l i p i n t e r f e r e n c e .

Others depend on t h e s p r i n g t e n s i o n t o u r g e t h e l i p

i n t o intimate shaft contact.

I n p r a c t i c e , a c a r e f u l balance o f i n t e r f e r e n c e ,

s p r i n g c h a r a c t e r i s t i c s and c o n t a c t band w i d t h must be a l l i e d t o knowledge o f the t y p e o f m a t e r i a l b e i n g used, b e a r i n g t ype, and c o n d i t i o n and o t h e r e n v i r o n mental c o n s i d e r a t i o n s such as t e mpe rat ure , f l u i d and,

i f any, pressure.

A t y p i c a l range o f sea l p r o f i l e s i s shown i n F i g . 4 w hich a l s o i l l u s t r a t e s exp e d ie n t used when i n s u f f i c i e n t space i s a v a i l a b l e t o accommodate a p a i r o f seals,

i.e.

t h e s o - c a l l e d d u s t l i p de si gn .

Fig.4

15.3

T y p i c a l se al p r o f i l e s .

MATERIAL

N i t r i l e - b a s e s y n t h e t i c rubber compounds a r e w i d e l y employed as standard mate r i a l s by reason o f t h e i r c o m p a t i b i l i t y w i t h most l u b r i c a t i n g o i l s and greases and t h e i r r e s i s t a n c e t o wear.

There a r e , however, c e r t a i n r o l l i n g o i l s and

c o o l a n t s wh ic h may cause e x c e s s i v e s w e l l o r s h r i n k a g e o f such polymers and a f l u o r o c a r b o n r u b be r,

e.g.

V i t o n , may be a necessary s e l e c t i o n .

This i s p a r t i -

c u l a r l y t r u e o f some palm o i l s o l u t i o n s and o t h e r s o l u b l e types o f o i l . C o n s i d e r a t i o n f o r o p e r a t i o n a l t emp era t u re i s important and, i t i s t h e c o n d i t i o n a t t h e l i p o f t h e s e a l which i s paramount

t h e e n v ir o n m e n t a l t e mpe rat ure .

However,

-

i n t h i s respect, not necessarily

i t may be s a i d t h a t n i t r i l e s a r e f r e -

q u e n t l y used w i t h success f o r i n t e r m i t t e n t s e r v i c e temperatures o f 15OoC and a r e c o n t i n u o u s l y r a t e d f o r 120°C

i n lubricated conditions.

Above these values

e i t h e r a c r y l i c r ubb ers, f l u o r o c a r b o n o r s i l i c o n compounds would r e q u i r e i n v e s t i gation. Many

s i l i c o n e and n i t r i l e rubber s h a f t s e a l s a r e f i t t e d i n automotive a p p l i -

c a t i o n s f o r c r a n k s h a f t and gearbox s e a l i n g ,

i n which areas much use i s b e i n g

made o f grooved s e a l i n g s u r f a c e s which a r e designed t o produce a hydrodynamic

356 e f f e c t i n the

oil film

b e i n g sealed, e f f e c t i v e l y causing t h e o i l t o be pumped

away from t h e s e al l i p (see F i g . 5 ) .

F ig . 5

Metal i n s e r t sea l w i t h hydrodynamic a i d .

D e t a i l e d m a t e r i a l recommendations a r e g i v e n i n Appendix 1 .

15.4

SEAL LUBRICATION

I n common w i t h most o t h e r forms o f dynamic s e a l , depend f o r t h e i r e f f i c i e n t and c o n s i s t e n t stable f l u i d f i l m .

r o t a r y s h a f t l i p seals

performance upon t h e presence o f a

The e s t a b l i s h m e n t o f t h i s f i l m , w hich w i l l t y p i c a l l y be i n

t h e o r d e r o f a few mi cro ns t hi ckn ess, may n o t o c c u r immediately, and i t i s n o t uncommon f o r a h i g h p erce nt ag e o f wear t o o ccur on r o t a r y s h a f t seal l i p s during t h i s p e r i o d b e f o r e s t e a d y - s t a t e c o n d i t i o n s a r e achieved.

For t h i s reason, i t

i s always good p r a c t i c e t o a p p l y a l u b r i c a n t t o t h e seal l i p and i n t h e seal c a v i t y before f i t t i n g . Where s i n g l e s e a l s a r e housed a t each end o f t h e housing, t h e r e i s n o r m a l l y s u f f i c i e n t b e a r i n g l u b r i c a n t i n c o n t a c t t o p r o v i d e adequate l u b r i c a t i o n . Again, where two s e a l s a r e housed t o g e t h e r ,

i t i s o f t e n found t h a t w i t h b e a r i n g l u b r i -

c a n t on one s e a l and e i t h e r r o l l i n g f l u i d o r r o l l c o o l a n t on t h e o t h e r , f u r t h e r l u b r i c a t i o n i s unnecessary.

I n a l l cases t h e l i b e r a l a p p l i c a t i o n o f grease t o

t h e s e a l s on assembly w i l l ensure l u b r i c a t i o n from t h e b e g i n n i n g and,

i n some

i n s ta n c e s , t h i s w i l l be found s u f f i c i e n t t o l a s t from one f i t t i n g t o t h e n e x t . However, t h e r e a r e many s e a l i n g arrangements, e s p e c i a l l y on r o l l i n g m i l l be a r in g s , and

i n which two o r more s e a l s a r e f i t t e d t o g e t h e r i n t h e same housing

t h e r e i s t h e danger t h a t a t l e a s t one w i l l r u n d r y u n l e s s l u b r i c a n t i s

s u p p l i e d from an e x t e r n a l source.

T h i s can b e s t be accomplished by d r i l l i n g a

h o l e t h r o u g h t h e chock c o n n e c t i n g w i t h an a n n u l a r groove i n t h e back o f t h e s e a l housing, as shown i n F i g. 6,

and u s i n g a s p e c i a l t y p e o f seal which has a

s e r i e s o f r a d i a l p o r t s i n t h e base f o r passage o f l u b r i c a n t t o t h e seal l i p . When i t i s d i f f i c u l t o r i m p o s s i b l e t o machine an annular groove i n t h e back o f t h e s e a l housing, shown i n F i g . 7 .

t h i s groove may be i n c o r p o r a t e d i n t h e s e a l s themselves, as

357

Fig.6

Seal l u b r i c a t i o n v i a i n s e a l base.

ports

Fig.7

Seal l u b r i c a t i o n v i a p o r t s and a n n u l a r groove i n seal base.

I n g e n e r a l , a good q u a l i t y m i n e r a l o i l o r grease i s s u i t a b l e f o r seal l u b r i c a t i o n , b u t molybdenised l u b r i c a n t s may be used t o advantage where a p p l i c a t i o n i s infrequent.

Care sh ou l d be taken t o ensure t h a t t h e grease o r l u b r i c a n t w i t h

which t h e s e a l

i s t o come i n t o c o n t a c t i s co mpatible.

are being

used w i t h d i u t e m i n e r a l a c i d s , b u t y l

For example, where s e a l s

compositions may w e l l be used.

T h i s m a t e r i a l i s l i k e l y t o s w e l l i n c o n t a c t w i t h m i n e r a l o i l o r grease and an a l t e r n a t i v e l u b r i c a n t w 1 1 be e s s e n t i a l .

15.5

SHAFT SURFACES

The s e a l i n g a re a o f t h e s h a f t sh ou l d be a f i n e ground f i n i s h o f 0.4 t o 0.8 pm (16

-

32 p i n . ) CLA or Ra f o r most a p p l i c a t i o n s , b u t f o r t h e h i g h e r speed range

i t i s recommended t h a t t h e s u r f a c e f i n i s h be improved t o 0.2

CLA o r Ra.

t o 0 . h pm ( 8 - 1 6 p I n )

I n a l l cases i t i s i m p o r t a n t t h a t t h e s h a f t s e a l i n g area be f r e e

from machining marks, d en t s, b u r r s and scrat ches. Where f l u o r o c a r b o n o r a c r y l i c

rubber s e a l s a r e b e i n g employed,

i t i s also

a d v i s a b l e t o use t h e f i n e r l e v e l o f f i n i s h i n d i c a t e d above i n o r d e r t o e l i m i n a t e p i c k - u p o f t h e s e al m a t e r i a l .

I f l u b r i c a t i o n i s adequate and f r e e f rom a b r a s i v e c o n t a c t , unhardened m i l d s t e e l s h a f t s w i l l g e n e r a l l y g i v e s a t i s f a c t o r y r e s u l t s under normal o p e r a t i n g conditions.

However, a h a r d e r s h a f t m a t e r i a l i s t o be p r e f e r r e d f o r a p p l i c a t i o n s

where l u b r i c a t i o n i s poor, a b r a s i v e s a r e p resent, o r speed and p r e s s u r e condit i o n s a r e p a r t i c u l a r l y arduous.

A f i n e machined f i n i s h i s s u i t a b l e f o r t h e housing bore.

358

15.6

FRICTION

The r u b b i n g f r i c t i o n o f t h e seal l i p on t h e s h a f t m a t e r i a l i n e v i t a b l y causes a h i g h e r l o c a l temperature than i s p r e s e n t i n t h e f l u i d b e i n g s e a l e d . e f f e c t w i l l be

This

due t o t h e i n t e r f e r e n c e o f t h e seal l i p on t h e s h a f t m a t e r i a l

and may be aggravated by inadequate l u b r i c a t i o n o r speeds i n excess o f t h a t f o r which a

p a r t i c u l a r seal was designed.

Assuming t h e system temperature t o be

w e l l w i t h i n t h e bounds o f t h e m a t e r i a l c a p a b i l i t y , a h i g h d i f f e r e n t i a l between l i p t i p temperature and f l u i d temperature w i l l be m a n i f e s t e d i n many cases by h a i r - l i n e scores i n t h e seal l i p c o - a x i a l w i t h t h e s h a f t .

Local c a r b o n i s a t i o n

o f t h e rubber compound w i l l a l s o be e v i d e n t . F i g u r e 8 i n d i c a t e s a s e t o f curves d e r i v e d by experiment, p r o j e c t i n g f r i c t i o n a l h o r s e power a g a i n s t s e a l d i a m e t e r f o r a c o n v e n t i o n a l r o t a r y l i p seal design o p e r a t i n g a t 500 r.p.m.

i n m i n e r a l l u b r i c a t i n g o i l a t d i f f e r e n t system

pressures.

300

LOO

500

600

700

800

900

Shaft diameter [ m m l Fig.8

F r i c t i o n a l horse power absorbed by r o t a r y s h a f t l i p s s e a l s , having c o n v e n t i o n a l l i p i n t e r f e r e n c e o p e r a t i n g a t 500 r e v h i n

359

15.7

SPEEDS

Many o f t h e f a b r i c - b a c k e d t y p e o f s e a l s t o g e t h e r w i t h those o f t h e m e t a l supported t y p e a r e w o r k i n g s a t i s f a c t o r i l y on 400 mm r o l l - n e c k d i a m e t e r s a t speeds o f up t o 25 m/s (5000 f t / m i n ) o v e r s u s t a i n e d w o r k i n g p e r i o d s . however,

many f a c t o r s such as s u r f a c e f i n i s h ,

There are,

e c c e n t r i c i t y , and l u b r i c a t i o n

which can l i m i t t h e maximum speed f o r which any seal i s s u i t a b l e , and manufact u r e r s should be c o n s u l t e d i n cases o f doubt.

15.8

ECCENTRICITY

Where p l a i n metal o r s y n t h e t i c c o m p o s i t i o n b e a r i n g s a r e b e i n g employed,

it

i s n o t uncommon t o f i n d t h a t t h e s h a f t i s n o t t r u l y c o n c e n t r i c w i t h t h e seal housing, owing t o b e a r i n g c l e a r a n c e and subsequent wear.

I n t h i s event,

it is

e s s e n t i a l f o r e f f i c i e n t s e a l i n g t h a t t h e seal l i p be capable o f f o l l o w i n g a l l s h a f t movement and,

indeed, on many l a r g e c o m p a r a t i v e l y slow-moving s h a f t s

e c c e n t r i c i t y values o f 2 . 5 mm have been s a t i s f a c t o r i l y accommodated.

Naturally,

t h e s e a l performance i n terms o f e c c e n t r i c i t y c a p a b i l i t y w i l l be speed and s h a f t diameter dependent. Where s p l i t s e a l s a r e f i t t e d , then p a r t i c u l a r c o n s i d e r a t i o n i s necessary t o t h e problem o f s h a f t e c c e n t r i c i t y , s i n c e t h e r e may be a tendency f o r a s p l i t seal t o open a t t h e j o i n . 15.9

PRESSURE

A l t h o u g h few r o t a r y s h a f t l i p s e a l s a r e spec f i c a l l y designed as s t a n d a r d compqnents t o accept s i g n i f i c a n t pressures, t h e use o f m e t a l - s u p p o r t i n g p l a t e s w i l l extend t h e u s e f u l n e s s o f t h i s t y p e o f s e a l

A t y p i c a l p r o f i l e i s shown ' i n

Fig.9.

Fig.9

Seal w i t h shaped s u p p o r t p l a t e f o r p r e s s u r e s up t o 3.0 b a r .

As a r e s u l t o f e x p e r i m e n t a l work on t h e s e a l i n g o f o i l - f i l l e d marine s t e r n glands

and manoeuvring t h r u s t e r s , a seal l i p p r o f i l e has been developed which

s a t i s f a c t o r i l y s u s t a i n s pressures up t o 4 . 0 b a r w i t h o u t t h e use o f a shaped support p l a t e .

The base must be f u l l y supported as i n d i c a t e d i n Fig.10.

360

Q Fig.10

New se al development f o r p ressures up t o 4.0 b a r w i t h o u t shaped su pp ort p l a t e .

Where c o n s t a n t a p p l i e d p r e s s u r e i s n o t a n t i c i p a t e d , ted t h a t g r e a s e - l u b r i c a t e d

i t i s f r e q u e n t l y sugges-

b e a r i n g s a r e equipped w i t h r e l i e f h o l e s and t h a t o i l -

l u b r i c a t e d b e a r i n g s have d r a i n s o f adequate s i z e .

D rains taken f r o m t h e ends

o f t h e b e a r i n g near t h e s e a l s w i l l h e l p t o d i s s i p a t e any l o c a l i s e d p r e s s u r e build - u p .

Where p o s s i b l e , st ep s sh ou l d be t aken i n b e a r i n g d e s i g n t o p r e v e n t

escaping h i g h p r e s s u r e o i l i mpi n gi n g d i r e c t l y upon t h e s e a l s . I n some cases where t h e loss o f a sma l l amount o f grease i s unimportant,

a

simple r e l i e f system may be formed by f a c i n g s e a l s away f r o m t h e b e a r i n g and a l l o w i n g t h e s e a l l i p t o be l i f t e d under t h e i n f l u e n c e o f t h e l u b r i c a n t pressure. 15.10

CARE AND HANDLING

F l u i d s e a l s sh ou l d be handled a t a l l t i mes w i t h extreme c a r e s i n c e t h e l i f e o f b e a r in g s o r o t h e r c o s t l y machine p a r t s may depend upon t h e i r e f f i c i e n c y . A t t e n t i o n t o the f o l l o w i n g v i t a l p o i n t s w i l l a s s i s t i n ensuring t r o u b l e - f r e e operation during service. 15.10.1 (i)

Storage The s t o r e

sh ou l d have a c o o l , c l e a n and d r y atmosphere,

f r e e from

d u s t and g r i t . (ii)

Whenever p o s s i b l e , s e a l s should n o t be removed from t h e wrapping i n which they were s u p p l i e d , as t h i s p r o v i d e s p r o t e c t i o n and i d e n t i f i c a t i o n

( i i i ) Avoid u n t i d y s t a c k i n g as t h e w e i g h t may d i s t o r t t h e s e a l s a t t h e bottom o f the stack. (iv)

Seals should never be t hre ad ed on w i r e o r s t r i n g as t h i s w i l l damage the l i p s .

361 15.10.2

(i)

H a n d lin g I t must be remembered t h a t seal l i p s a r e extremely v u l n e r a b l e t o damage

and t h e s m a l l e s t n i c k p r o v i d e s a p o t e n t i a l l e a k p a t h . (ii)

Seal r e i n f o r c i n g i n s e r t s , a l t h o u g h adequate f o r t h e i r d u t y , may deform under adverse h a n d l i n g o r s t a c k i n g .

( i i i ) Seals h avi n g met al o u t s i d e surf ace s may damage o t h e r s e a l s , e s p e c i a l l y

i f the met al edges c o n t a c t t he ru bb er p a r t s o f n e i g h b o u r i n g seals. 15.10.3

Fitting

A h i g h p r o p o r t i o n o f f a i l u r e s and leakage o f o i l s e a l s i s due t o i n c o r r e c t f i t t i n g r e s u l t i n g i n damage t o b o t h se al and s e a l i n g s u r f a c e .

S t r i c t attention

t o t h e f o l l o w i n g m a t t e r s i s e s s e n t i a l i f b e s t performance i s t o be obtained. (i)

Before f i t t i n g ,

t h e se al should be examined t o ensure t h a t i t i s clean

and undamaged. (ii)

The s e a l i n g l i p sh ou l d be smeared w i t h s u i t a b l e c l e a n l u b r i c a n t . Seals used as d u s t e x c l u d e r s should be packed w i t h a compatible grease.

( i i i ) The s e a l i n g l i p , n o r m a l l y , sho ul d f a c e t h e f l u i d t o be sealed. When f i t t i n g ,

i t i s i m p o r t a n t t o ensure t h a t t h e s e a l i n g l i p i s n o t

damaged even by

the s l i g h t e s t n i c k , t h a t the s p r i n g i s c o r r e c t l y

l o c a t e d when i n p o s i t i o n , and t h a t t h e seal i s p r o p e r l y pressed home i n t o t h e h ou si ng re cess. Examine t h e s h a f t which should be f r e e from a l l roughness and sharp edges and a v o i d pa ssi ng t h e s e a l i n g l i p over keyways, screw threads, o r shoulders.

S h a f t edges o r sho ul d ers should be w e l l rounded o r

chamfered, and where t h i s i s n o t p r a c t i c a b l e a f i t t i n g sleeve s l i g h t l y l a r g e r t h an t h e

s h a f t w i t h a l e a d - i n t a p e r should be used.

A c c o r d ing t o t h e t yp e o f assembly,

i t may be necessary e i t h e r t o f i r s t

p r e s s t h e se al i n t o t h e h ou si ng and subsequently o n t o t h e s h a f t o r , alternatively,

t o pass t he se al ove r t h e s h a f t and then press i t i n t o

t h e h o u si ng . I t i s p r e f e r a b l e f i r s t t o mount t h e seal on t h e s h a f t where circumstances p e r m i t , s i n c e t h i s a l l o w s o b s e r v a t i o n o f t h e l i p d u r i n g assembly. ( v i i ) The assembly sh ou l d n o t be al l o we d t o r e s t f o r any l e n g t h o f t i m e a t an in c o mpl e t e s t a t e o f f i t t i n g , where the w eight o f t h e s h a f t o r housing may be borne by t h e s e a l ,

r e s u l t i n g i n damage o r d i s t o r t i o n t o the

latter. ( v i i i ) W h e n p r e s s i n g t h e se al i n t o t h e housing, a u n i f o r m p r e s s u r e should be e x e r t e d , p r e f e r a b l y by suitable tool.

means o f an a r b o r press i n combination w i t h a

The d i ame t e r o f t h e t o o l should be s l i g h t l y s m a l l e r

than the diameter o f t h e h ou si ng by 0.1

t o 0.4 mm.

The o u t s i d e surface

362

of the seal can be smeared with a suitable lubricant in order to facilitate fitting. Care must be taken to ensure that the seal does not enter the housing recess in a tilted position, since this will cause damage to the outer surface.

SERVICE PROBLEMS AND THEIR SOLUTIONS

15.11

A number of fault-finding procedures follow which, if taken in sequence, should analyse the reason for a given difficulty with rotary shaft lip seals.

15.11.1

Unacceptable Leakage

This is almost always associated with oil lubricated bearings, since grease is not

a

difficult lubricant to seal. The term "unacceptable" can have wide

interpretation since an occasional drop of oil might be disastrous if it resulted in contamination of the product being handled by the machine concerned in such spheres as the textile, paper, or food industries, whereas it would probably remain unnoticed in a heavy industrial environment. Since the vast increase in

oil prices there is, however, a greater sensiti-

vity to oil losses in any form and leakage rates that hitherto have been ignored are now becoming regarded as unacceptable. When dealing with such complaints it is essential to discover the history of equipment concerned, and this broadly

(I)

falls into three categories:

New equipment recently commissioned, where sealing has been regarded as unsatisfactory from the start.

(11)

Equipment that has been in operation for a period of time and only recently has developed leakage problems.

( I l l ) Equipment that was satisfactory

during its first term of operation but

leakage has occurred after fitting replacement seals during routine maintenance or overhaul. Since trouble tracing is basically a process of eliminating of substantiating faults, the sequence of checks required would vary with each of the above

categories. In order to simp1 ify the procedures and'avoid

irrelevant investigations, the

recommended sequences for each of the above categories is defined by letter symbols to be used in conjunction with the attached fault-finding chart. Category ( ) Full checks in order as A, B, C ,

D and

E until fault is discovered.

Category ( I 1 A, B, C ( 1 ) ,

D ( 2 ) , and D ( 3 ) .

If faults as C ( 1 ) o r D(2) are exhibited, ascer-

tain Deriod o f service with seals. This should be calculated in terms of hours

363 o f r u n n i n g and r e l a t e d t o speed, t e m p e r a t u r e , and o t h e r e n v i r o n m e n t a l c o n d i t i o n s

A moderate speed w i t h good c l e a n l u b r i c a t i o n c o n d i t i o n s and ambient temperat u r e s would n o r m a l l y a n t i c i p a t e a seal

l i f e o f around 10,000 h o u r s .

H i g h speeds, p o o r l u b r i c a t i o n , e l e v a t e d temperatures,

o r p a r t i a l l y abrasive

media c o u l d reduce t h i s t o as l i t t l e as 2,000 h o u r s . The p r o b l e m may t h e r e f o r e be

s i m p l y t h a t o f b e i n g due f o r s e a l replacement.

I f f a u l t s as i n (D3) a r e i n e v i d e n c e , o b t a i n d e t a i l s o f a l l media i n c o n t a c t w i t h seal

( i n c l u d i n g any c l e a n i n g f l u i d s ) as a change o f l i p m a t e r i a l may be

necessary t o o b t a i n c o m p a t a b i l i t y . I f s e a l s d i s p l a y no f a u l t s , check f o r mechanical d e f e c t s as E ( 1 ) and E ( 2 ) . Category A,

B, C( F a u l t - f i n d i n g Chart

(A)

I s leakage a c t u a l l y o c c u r r i n g f r o m t h e s e a l o r does i t stem f r o m such

sources as b e a r i n g c o v e r f l a n g e s and i s m e r e l y " c o l l e c t e d " housing,

g i v i n g a f a l s e impression?

by t h e s e a l

Check by w i p i n g c l e a n a l l a p p r o p r i a t e

a r e a s and r u n machine t o a s c e r t a i n leakage s o u r c e . (B)

I s l e a k a g e f r o m around s e a l back o r f r o m t h e l i p a l o n g t h e s h a f t ?

wiping (C) I f O / D (1)

b o t h c l e a n and o b s e r v i n g w h i l e machine i s leakage

-

Check by

running.

check t h e f o l l o w i n g :

Is s e a l a good f i t i n h o u s i n g o r i s i t s l a c k ? (On s p l i t s e a l s a s l a c k s e a l w i l 1 d i s p l a y a gap between s e a l e n d s ) .

( 2 ) I f h o u s i n g b o r e i s c o r r e c t s i z e t h e n s e a l O / D dimension i s suspect i f s l a c k i n housing. ( 3 ) I f s e a l i s good f i t i n h o u s i n g , check f o r damage on h o u s i n g b o r e .

(4) Check

h o u s i n g d e p t h t o e n s u r e s e a l i s b e i n g a x i a l l y compressed - i f

applicable. (0 )

If

leakage a l o n g s h a f t , check t h e f o l l o w i n g :

( 1 ) S h a f t s i z e , s u r f a c e f i n i s h , s h a f t damage a t c o n t a c t a r e a . ( 2 ) If ( 1 ) O . K . , ing.

check c o n d i t i o n o f s e a l i n g l i p f o r h a r d e n i n g and/or c r a c k -

I f e i t h e r i n e v i d e n c e , t h e n speed o r t e m p e r a t u r e c o n d i t i o n s a r e

probably incompatible w i t h seal m a t e r i a l .

( 3 ) I f l i p i s s o f t o r s w o l l e n t h i s i s u s u a l l y an i n d i c a t i o n o f chemical i n c o m p a t i b i l i t y w i t h t h e media i n c o n t a c t w i t h t h e s e a l .

(4) I f

( 2 ) and ( 3 ) O.K.,

check s e c t i o n w i d t h o f s e a l w i t h s p r i n g f i t t e d .

364 T h i s s h o u l d be a t l e a s t nominal s e c t i o n +1% immediately on removal and i n c r e a s i n g t o nominal

+3% a f t e r

one hour i n f r e e s t a t e .

S p r i n g may be

shortened by up t o 5% o f i t s o r i g i n a l l e n g t h i f s e c t i o n appears inadequate. (E)

I f checks

S e c t i o n measurement sho ul d be average o f

4

e q u i - d i s t a n t readings.

(C) and (D) do n o t r e v e a l any f a u l t s t h e problem may be due t o

mechanical c o n d i t i o n s and t h e f o l l o w i n g should be checked:

( 1 ) S h a f t t o h ou si ng con cen t r c i t y s h a f t and ho usi n g b o r e a t

4

-

check by means o f c a l i p e r s between

p o i n t s around p e r i p h e r y .

V a r i a t i o n s o f more

th a n 0.3 mm r e q u i r e f u r t h e r i n v e s t i g a t i o n . (2) I f s m a l l e s t c a l i p e r measurement o c c u r s between bottom o f s h a f t and housing, t h i s may i n d i c a t e b e a r i n g wear w i t h r e s u l t a n t dynamic e c c e n t r i city.

(Applicable t o horizontal shafts only).

( 3 ) I f b e a r i n g i s O.K. t he n ho usi n g o f f s e t may be r e s p o n s i b l e .

Seal housings

a r e n o r m a l l y c e n t r a l i s e d w i t h t h e s h a f t by means o f a machined r e g i s t e r w i t h th e b e a r i n g ho usi n g.

Where t h i s f e a t u r e

i s n o t i n c o r p o r a t e d then

i t may-be p o s s i b l e t o c e n t r a l i s e t h e housing by s l a c k e n i n g t h e b o l t s and repos i t on i ng .

(4)

I f (11,

( 2 ) and (3) a r e blameless t h en t h e f o l l o w i n g r e q u i r e s i n v e s t i -

gation:

I f bear ngs a r e o i l p r e s s u r e l u b r i c a t e d i s t h e r e adequate drainage t o prevent pressure build-up against the seal?

I f equipment op era t e s on a c o n s t a n t o i l l e v e l p r i n c i p l e , wheels o r b a l l - j o u r n a l

a r e t h e r e gear-

b e a r i n g s i n c l o s e p r o x i m i t y t o t h e seal causing

o i l turbulence or flooding? Where

the l a t t e r s i t u a t i o n exists,

t h e housing lands should be o n l y

m a r g i n a l l y l a r g e r t ha n s h a f t d i ame t e r i n o r d e r t o form a b a f f l e o r , alternatively,

a b a f f l e p l a t e f i t t e d between b e a r i n g and seal housing.

A temporary remedy can be made by u s i n g a 2.5 mm CAF gasket a t t h e bottom o f

the housing, t h e I / D o f which sho ul d be s h a f t diameter p l u s 0.5 nnn maximum.

A

f u r t h e r gasket o f equal t h i c k n e s s sh ou l d be f i t t e d underneath the r e t a i n i n g p l a t e t o restore the correct s e a l s (see F ig . 1 1 and F i g . 1 2 ) .

amount o f a x i a l compression i n t h e case o f r e t a i n e d

365

Fig.11

Showing how t o o l a r g e b o r e d i a m e t e r o f s e a l h o u s i n g l a n d p e r m i t s h i g h v e l o c i t y o i l impingement on s e a l .

B a f f l e p l a t e between b e a r i n g reduce r i s k o f o i l leakage.

and s e a l o r c l o s e - f i t t i n g s e a l would

.A.F gasket .5mm thick

Fig.12

Showing how f i t t i n g o f C.A.F. g a s k e t s can p r o v i d e a temporary remedy f o r s i t u a t i o n i n F i g . 1 1 .

( W i t h acknowledgement t o t h e l a t e Mr.Ray B l a d w i n - S e n i o r A d v i s o r y E n g i n e e r , rotary shaft l i p seals

-

who c o m p i l e d much o f t h e d a t a p r e s e n t e d h e r e ) .

366 APPENDIX 1 ROTARY SHAFT L I P SEAL F(ATERIAL RECOMMENDATION CHARTS The accompanying c h a r t s show v a r i o u s l u b r i c a n t s and r o l l i n g f l u i d s t h a t a r e commonly used i n t h e metal r o l l i n g i n d u s t r y .

Some o f these a r e n o t c h e m i c a l l y

c o m p a t i b l e w i t h t h e standard n i t r i l e rubbers used i n r o t a r y s h a f t l i p seal p r o d u c t i o n , and i t i s t h e r e f o r e necessary t o employ an a l t e r n a t i v e rubber compound t o achieve s a t i s f a c t o r y r e s u l t s i n terms o f s e a l e f f i c i e n c y and l i f e .

Seal L i p s The rubber compound i n t h e column headed " 1 s t choice"

i s t h e grade l e a s t

a f f e c t e d by t h e media concerned and should be s e l e c t e d wherever p o s s i b l e .

In

most i n s t a n c e s a second c h o i c e i s g i v e n and t h i s rubber can be used w i t h o u t serious detriment t o the seal. Where f l u o r o c a r b o n rubber (denoted by t h e l e t t e r 'A') appears as t h e o n l y c h o i c e , please n o t e t h a t none o f t h e c o n v e n t i o n a l commercial grade rubbers can be used as an a l t e r n a t i v e .

I n i n s t a n c e s where f l u o r o c a r b o n rubber appears as

t h e second c h o i c e i t i s u s u a l l y f o r economic reasons,

i n d i c a t i n g t h a t i t i s only

m a r g i n a l l y s u p e r i o r t o t h e commercial grade compound g i v e n as f i r s t c h o i c e , and t h e small advantage would o f t e n n o t j u s t i f y t h e a d d i t i o n a l c o s t . Seal Backs Although w i t h some media t h e seal back

f a b r i c m a t e r i a l s used f o r c o n s t r u c t i o n o f t h e

s u f f e r l i m i t e d v o l u m e t r i c change,

the effects are not detrimental t o

s e a l i n g e f f i c i e n c y as t h i s p a r t o f t h e s e a l i s f u l l y housed and n o r m a l l y a x i a l l y restrained. Selection o f Materials In r o l l i n g - m i l l applications,

r o t a r y s h a f t l i p seals a r e normally required t o

seal n o t o n l y a g a i n s t b e a r i n g l u b r i c a n t s b u t a l s o r o l l i n g f l u i d s ,

be taken t o s e l e c t a m a t e r i a l which i s c o m p a t i b l e w i t h both.

and c a r e should

T h i s may i n v o l v e

some compromise by s e l e c t i n g a second c h o i c e m a t e r i a l f o r e i t h e r t h e l u b r i c a n t o r the r o l l i n g f l u i d ,

i n o r d e r t o o b t a i n a reasonable degree o f c o m p a t i b i l i t y

w i t h both. I n d u a l s e a l i n g arrangements employing back-to-back

s e a l s , should o n l y one o f

t h e media n e c e s s i t a t e f l u o r o c a r b o n r u b b e r , t h e opposing s e a l c o u l d be made w i t h a l e s s c o s t l y c o m p a t i b l e grade o f rubber p r o v i d i n g t h a t c a r e i s taken i n i d e n t i f i c a t i o n and f i t t i n g . For convenience, rubbers, and

l e t t e r symbols a r e used i n t h e c h a r t s t o i n d i c a t e v a r i o u s

t h e key t o these i s g i v e n :

367 KEY TO MATERIAL CODES Code

Base r u b b e r compound

F I uorocarbon High n i t r i l e Medium h i g h n i t r i l e N i t r i le N i t r i l e with graphite N i t r i l e w i t h p a r a f f i n wax

RECOMMENDED SEAL LIP MATERIALS FOR USE WITH BEARING OILS AND GREASES Seal l i p m a t e r i a l s Brand Name o r Number

1 s t Choice

2nd Choice

B.P.

HCT 80

C

E

B.P.

Sperno 350 HB 'I 450 HB

C

D

B.P.

Energol GR 125-XP

C

0

E

C a s t r o l 98

C

CLP 1 1 4

C

E

C a l y s o l Grease

C

A

C

Duckhams Zero O i l

D

EP 69 O i l

C

D

EP 80 Gear L u b r i c a n t

D

C

Esso E s t i c 65

C

A

Esso Nuray 146

C

A

Esso Pen-0-Led

D

C

EP3

Fuchs MR 40

C

F

Mobi 1 Exu 66/25

C

D

C

F

C

E

C

E

" II

Vacuol i n e ' A A ' 'I 25 x 25R

I,

I'

Heavy

C

E

I'

Mobi l u b e H.D.90

C

E

"

Mobi l e x EP2 Grease

C

F

OM 100 O i l

C

A

Regal Gear O i l

C

B

S h e l l O i l 1624 and 1611

B

C

,I

II

I

EE"

"

Carnea

C

B

"

Faunus ' B '

B

A

I'

Macoma

D

C

"

Nassa 78

C

A

Seal l i p m a t e r i a l s f o r b e a r i n g o i l s and greases (contd.) Seal l i p m a t e r i a Brand Name o r Number

1 s t Choice

2nd C Dice

C

A

Teressa

C

A

"

T i v e l a 75

C

D

"

V i t r e a 75

C

B

"

R e t i n o x Grease

A

C

She1 1 Telona 945 'I

'I

Donax 17

C

B

I'

Aeroshel 1 Grease No.7

C

A

Oil

C

D

Ucon

A l o - J idac

A

Caster O i l ( w i t h w a t e r ) I, I' ( w i t h methyl a t e d

A

B

C

E

C imcoo 1

E

A

Cirncool E 5

B

C

Castrol

A

B

B

A

spirit)

Coolage SL

Croda D4 A Lubrotex

'I

1;

7804

A

Dasco 900

B

A

Esso Somentor N35

C

A

'I

w20

A

6

I'

33 and N60

A

C

I,

,I

Univis ~ 5 8

I'

C

B

-

Emulsion KF 81

A

Germ K i n e t r o l FR3A

A

-

G u l f Mineral Seal

C

D

I'

Cut O i l

C

D

"

93

C

D

B

A

Houghton Permasol

k

B

H u i l e de Laminage 102 P & 982 R

B

C

Hydr i t

B

D

KF 61 R o l l i n g Oil

A

D

Lubricor ' T I

B

E

"

S u l f o n a ED

S

369 Seal l i p m a t e r i a l s f o r r o l l c o o l a n t s and r o l l i n g o i l s ( c o n t d . ) Seal l i p m a t e r i a l s Brand Name o r Number

1 s t Choice

Mobil Generex 56, 57 and 404D 11 11

"

22 and 24

11

322

A

B

C

B

C

D

P r o s o l 66

A

B

44

B

A

11

33

A

Solvac 11

A

-

B

A

II

'I

2nd Choice

~

~~~

11

11

a00 and "BB"

C

B

M i r o b o 415A

B

A

Ocut G

C

A

Palm O i l

B

A

Quaker T i n n o l 12

E

D

B

D

B

A

B

A

V a c t r a "HH"

I'

11

109

I1

'I

I,

Quakerol 41 ( w i t h S h e l l Carnea 31) 43, 82, a7 M and

88-182 M I'

Qwerl 506

Rol l u p 200 S h e l l Dromus

B

B

D

B

A

B

A

C

B

'I

1270/1307

B

A

I'

1076

D

C

Tayol 316 Emulsion

B

A

Texaco Texatherm 320

A

C

S t e r n o l PL106 and PL107

T r e l l u b 12 A

B

A

Wyrol H40

C

A