tribology of miniature systems tribology series 13

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0.60

+ 0.40 c a u LL

Q) 0 u

c

.- .-J

Le- 0.20

.- a 0.10 Ti 0.08 tk 0.06

0.04

.-I

journal alignment (within 1 ,urn), and longer life, since the wear

debris are collected in the corners ("pockets") of the bearing

hole. The more sides the polygon has, the greater the change in

the friction coefficient as a function of the load direction (refs.

3 4 3 , 3 4 6 ) . The friction coefficient of prismatic bearings can be

3-5 times lower and their bearing life as much as 50 times longer

than those of cylindrical bearings (refs. 3 4 2 , 3 4 5 ) .

- .

-

- - - -

1

63.3mm2/5

52.3 mm2/5

50 mm2/s

0.02 I I 1 1 1 I I I c b.02 0.04 0.060.08D.(O 0.2 0.4 0.6 0.0 1.0

Contact pressure, MPa

F ig . 5 . 6 . Minimum value o f the f r i c t i o n c o e f f i c i e n t i n m i n i a t u r e porous bear ings as a f u n c t i o n o f con tac t pressure a t va r ious r e l a t i v e bea r ing c learances (p) and v i s c o s i t i e s o f o i l used (7) ( r e f . 3 4 0 ) .



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C a p i l l a r y - b e a r i n g s , 439 - e f f e c t , 368 - method, 336

Carbon-graphi tes , 18 , 143, 2 0 9 , 438 - c o u n t e r f a c e s f o r 143

Carbur iz ing , 290 Card machines, 288, 289, 450 C a t a s t r o p h i c wear of ceramics,

C a t h e t e r systems, 500 Cent re b e a r i n g s , 4 2 8 Ceramics, 1 6 , 134, 208, 448 Chain d r i v e s , 4 6 2 Charnley p r o s t h e s i s , 496 Chem i c a1

138

- n i c k e l i n g , 285 - s t a b i l i t y of o i l , 243 - vapour d e p o s i t i o n (CVD) ,

292 Chromizinq, 285, 290 Cleaning, 230, 381 C l e a n l i n e s s e v a l u a t i o n , 231,

386 Clearance, 407 Clock - o i l s , 34 - type b e a r i n g s , 73, 1 4 9 , 4 0 4 - l u b r i c a t e d , 1 4 9 - u n l u b r i c a t e d , 73, 404

Clu tches , 463 Coat ings , 4 4 , 269 - a n t i - f r i c t i o n , 269 - a n t i - m i g r a t i o n , 2 1 6 - ant i -wear , 285 - on f a s t e n e r s , 284 - l u b r i c a t i o n , 281 - t r a n s f e r r e d , 279, 447

Cobalt-based a l l o y s , 11 Cohesive energy d e n s i t y , 97 Cold polymer iza t ion , 263 Collector, 472 Compat ib i l i ty - of o i l s and materials, 51, - of s o l v e n t s and materials,

198, 2 6 1 , 371, 376

383 Composites, 1 6 Computer - analyzed microscopic i n t e r - - d e v i c e s , 481

ferometry (CAMI) , 4 9 1 Conica l b e a r i n g s , 424 Connector t r a n s m i s s i o n s , 4 6 2 Contac t a n g l e , 354 Contac ts , 467 Contaminants, 386, 401, 4 4 6 Conversion c o a t i n g s , 289 Copper-based a l l o y s , 1 0 , 80 ,

1 4 4 , 2 9 6

Corros ion , 1 3 , 385, 490 - i n h i b i t o r s , 43 - of magnet ic media, 490 - of o i l s , 53, 376 - of s o l v e n t s , 385

Corros iveness

Corundum, 1 5 Couplings, 463 Cover p l a t e t h r u s t b e a r i n g s ,

Cracking a c i l i t y of polymers,

Creeping of o i l s , 2 1 2 Cryogenic tempera ture materials,

C y l i n d r i c a l b e a r i n g s , 404, 4 2 7

429

377, 383

8

Damping of o s c i l l a t i o n s - curve , 303 - o i l s , 4 7 , 456

Degradat ion of l u b r i c a n t , 161 Densi ty e s t i m a t i o n methods, 362 Depos i t ing a n t i - m i g r a t i o n coa t -

i n q s , 2 2 6 , 230 Detec t i n g - contaminants , 231, 386, 4 0 1 - epi lame and l u b r i c a n t f i l m s , - running-in p e r i o d , 165, 395

Detonat ion-sprayed c o a t i n g s , 287 Diamond, 1 6 , 145 Diaspore, 1 4 1 Dicha lconides , 69 Dielectric c o n s t a n t

234, 381, 390, 478

- of o i l s , 52 - d e t e r m i n a t i o n , 364 - of polymers, 20 256

Diesel engine i n j e c t i o n pumps,

Disk f i l e memories, 481 Drives, 453 Drop weight method, 353 DuprB's e q u a t i o n , 213 D i i r r ' s a p p a r a t u s , 372 Dustproof t e s t i n g , 4 0 1 Dynamics o f l i q u i d s p r e a d i n g ,

2 1 2

Earnshawls theorem, 437 Edge e f f e c t , 2 1 4 E f f e c t - of climate on l u b r i c a t i o n ,

46, 208, 256 - of e lec t r ic f i e l d on f r i c t i o n and wear, 504 - of l u b r i c a n t on polymer, 261 - of magnet ic f i e l d on f r i c t i o n and wear, 503 - of polymer an lubricant, 265, 371



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as one to two orders of magnitude, so that it is difficult to as-

sign a specific value to the abrasive constant K for a given paper.

The similarities between paper and ribbon wear suggest that the

nature of the wear process is also similar, i.e. the wear is caused by

abrasion. This was confirmed for woven printer ribbons impregnated

with liquid ink (ref. 823). The wear of un-inked fabrics or ribbons

was found to be typically two to three orders of magnitude smaller

than the wear of inked fabrics. Since the major constituents of

ribbon inks are frequently materials known to lubricate and reduce

wear, such as mineral oils, oleates and oleic acid, ribbon wear

does not have an adhesive character, Abrasive wear by paper or rib-

bon results from small amounts of sub-micron size abrasive particles

in them. An increase in humidity results in the wear of the ribbon

increasing with almost a square root relation. Abrasive wear by

ribbons obeys the elementary relation for this kind of wear.

can vary by over two orders of magnitude (refs. 280, 823). The ma-

jor difference in the relative abrasiveness of different papers

and ribbons is to do with difference in the size rather than the

amount of their abrasive particles. Their abrasiveness is also

strongly dependent on prior use and humidity. In the relative hum-

idity range of 10-60% the abrasiveness can change by as much as a

factor of ten for paper and a factor of two for ribbons. After mil-

tiple use, the abrasiveness of both materials can dramatically

decrease, by up to one to two orders of magnitude after ten or so

passes. To investigate the ability of paper and ribbon to generate

wear and other materials to resist such wear, a piece of apparatus

is needed which provides a large amount of unused surface area of

paper or ribbon. The apparatus developed by Roshon for this purpose

(ref. 824) basically consists of a large circular drum with the

paper or ribbon specimen mounted on the drum's periphery. The drum

rotates, while a wear specimen slowly moves across the surface of

the drum in the direction of the drum axis, which effectivelygives

a helical wear path.

The abrasiveness of commercially available papers and ribbons

The abrasiveness of both paper and ribbon increases when ex-

ternal abrasive media become attached to their surfaces. This is

also true of magnetic media which are themselves very abrasive and

provide a similar wear situation to that of paper and ribbon. The

aspect of contamination is very significant since computer systems

are more and more frequently used in stores and factories (ref.

796). In such conditions the external abrasive may predominate and



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the greater its effect on the computational friction coefficient.

The ratio of the maximum to the minimum value of the computational

friction coefficient as a function ofKis shown by Pig. 9.7 c and

d.

The bearing clearance also has an effect on the frictional

torque of the bearing. The experimentally determined frictional

torque regression formula for cylindrical and prismatic miniature

journal bearings with a sintered porous bronze bush is expressed

by eqn. (5.8)(refs. 341, 343). The spread of the frictional torque

SM at the spread of the bearing clearance S y can be estimated using

the following formula:

(9.37)

where Mf is the frictional torque, and u/ the relative clearance.

k = 2, we obtain from eqn. (9.37) that

After the differentiation of eqn. (5.8) uponyand assuming that

(9.38)

Taking into consideration that for bearings with cylindrical

sintered porous bronze bushes the value of parameter a is up to

16 times greater than for similar prismatic bearings (refs.341-343)

and assuming that the values of a. (see eqn. (5.8)) are aoc and

a for cylindrical and prismatic bearings respectively (the value

of aoc is slightly greater), the following expressions canbe found:

for cylindrical bearings

OP

1 6ac M f c = a + -

Y 2 oc

and for prismatic bearings

(9.39)

(9.40)

(9.41)

(9.42) - 2a

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2 1 6

The f i r s t method w a s i nven ted by Woog i n France i n t h e n i n e t e e n

t w e n t i e s , t h e second method w a s developed i n U S Navy l a b o r a t o r i e s a f t e r t h e l a s t w a r , and t h e chemical t r e a t m e n t method w a s i nven ted

by Osowiecki and a p p l i e d i n i n d u s t r y i n S w i t z e r l a n d i n 1 9 6 4 .

The c o a t i n g ( ep i l ame) i s l a i d on t h e s o l i d s u r f a c e from l i q u i d

o r g a s s o l u t i o n ( o r d i s p e r s i o n ) . The t h i c k n e s s of t h e l a y e r u s u a l l y

does n o t exceed 0 . 5 ,urn. The a c t i v e p o l a r groups o f t h e ep i l ame

macromolecules a r e p h y s i c a l l y adsorbed o r chemisorbed on t h e s o l i d

s u r f a c e . Osowiecki 's method is ve ry e f f e c t i v e i n t h e case o f m i n e r a l

s o l i d s u r f a c e s . The e f f e c t of t h e chemical t r e a t m e n t of t h e s u r f a c e

i s v e r y s t a b l e and f o r example, u l t r a s o n i c c l e a n i n g o r chemical i n -

t e r a c t i o n s between t h e o i l and t h e m a t e r i a l o f t h e s u r f a c e l a y e r do

not change t h e e n e r g e t i c a l p r o p e r t i e s o f t h e s u r f a c e . Only s t r o n g

a l k a l i s o r a c i d s can s p o i l t h e t r e a t e d s u r f a c e l a y e r o f ruby o r

s a p p h i r e j e w e l s . Osowiecki ' s method h a s been a p p l i e d by Reno S.A.

and by KIF Parechoc i n Swi t ze r l and t o p r e v e n t o i l m i g r a t i n g from

t h e rubb ing r e g i o n of t h e cove r b e a r i n g i n t h e watch b a l a n c e , e s p e -

c i a l l y i n t h e I n c a b l o c system.

6 . 2 . 4 . COATINGS (EPILAMES)

The r equ i r emen t s f o r t h e s p e c i a l c o a t i n g s ( e p i l a m e s ) t o p r e v e n t

o i l from s p r e a d i n g or c r e e p i n g are as follows ( r e f . 3 9 0 ) :

1) Low s u r f a c e f r e e ene rgy ,

2 ) S t r o n g adhesion t o t h e s o l i d s u r f a c e ,

3 ) High chemical s t a b i l i t y ,

4 ) The c o a t i n g compound must be i n e r t t o t h e o i l and t h e c o a t e d ma-

t e r i a l s ' 5 ) Broad t empera tu re r ange o f u se ,

6 ) S u i t a b l e ha rdness and s h e a r s t r e n g t h ,

7) Homogeneity o f t h e c o a t i n g l a y e r on t h e whole so l id s u r f a c e

( t h i c k n e s s , mechanical and physicochemical p r o p e r t i e s ) , 8 ) The s m a l l e s t p o s s i b l e t h i c k n e s s ,

9 ) The compound f o r t h e ep i l ame shou ld be s o l u b l e i n common s o l -

v e n t s ,

10) The t e c h n i q u e s f o r d e p o s i t i n g c o a t i n g s must n o t be t o o s o p h i s t i -

c a t e d .

The s u r f a c e f r e e energy o f t h e ep i l ame depends on t h e chemica l

s t r u c t u r e of t h e macromolecules. The s u r f a c e free energy o f t h e

epi lame d e c r e a s e s f o r t h e macromolecules w i t h s i d e c h a i n s o f t h e

f o l l o w i n g s t r u c t u r e s ( r e f . 387) :



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of the i n c l i n e angle of t h e p l a t e 3 t h e pendulum kept by t h e f r i c -

t i o n torque devia tes f o r t h e angle 9 a t t h i c h the pendulum weight moment i s h igher than the f r i c t i o n torque. The value of t h e angle

'f can be read on t h e scale 7 on which t h e l i g h t beam r e f l e c t e d by

t h e mir ror 1 2 i s focussed.

1

F ig . 8.76. Device for studying t r i b o l o g i c a l p r o p e r t i e s o f m i n i a t u r e bearings i n a con- t r o l l e d environment. 1 - pendulum system, 2 - k n i f e bear ing, 3 - p l a t e , 4 - prisms, 5 - l e v e l mechanism, 6 - knob, 7 , 9 - scales , 8.11 - te lescopes, 10 - te lescope i l l u m i n a t o r , 12,13 - m i r r o r s , 1 4 - cover, 15 - extenso- meters, 16 - bearings being t e s t e d , 17 - push- e r , 18 - spheres ( r e f . 6351.

The i n c l i n a t i o n angle of t h e p l a t e 3 v a r i e s s lowly, e .g . 0 . 5

rad/min, and t h e pendulum acce le ra t ion is p r a c t i c a l l y 0 . The equa-

t i o n of reduced f r i c t i o n torque

M f = G L

f o r t h e bear ings being t e s t e d is

s i n ( 8 . 5 8 )

The angle of devia t ion of t h e pendulum is given by

s 'P'E (8 .59 )

where: S is t h e displacement of t h e l i g h t beam r e f l e c t e d by t h e

mirror 13 and read on t h e s c a l e 9 , D is t h e d i s t ance between the

mir ror and t h e s c a l e and G and L a r e t h e pendulum weight and length

r e spec t ive ly .


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pin-on-disk (ring) system; the PVC ring was machined from a 150 m

diameter pipe. The lowest wear occurred in the PA 66-PVC combina-

tion, while in the PTFE-PVC and PVC-PVC systems the wear was ap-

proximately 15 and 100 times higher respectively (ref. 231). When

PA 66 slides on PVC, it transfers a thin film onto the PVCsurface.

The PVC-PVC and PA 66-PVC systems have definite transition points

where the wear regimes change from low to catastrophic wear rates.

The transition point for a specific wear track length and ambient

temperature can be defined by the relationship P = Po - kN, where P is the applied load, Po the value of load where the linear graph

intersects the P-axis, N the number of passes per unit time and k

the gradient of the load-speed graph in the linear range.

When a rotating roller made of PTFE rubs against PTFE, PCA,

PETP, PE and PP films (at contact pressure 100 Pa and sliding speed

0.075 m/s), the rollers wear rate decreases in the above order of

counterface materials, i.e., the wear of the PTFE roller is 2.5

times higher when rubbing against a PTFE film than when rubbing

against PP film (refs. 232, 233). When the thickness of the poly-

mer film is increased from say 50 to 250 ,um, the wear rate de-

creases hyperbolically. The transferred layer of PTFE material de-

creases simultaneously from about 0.4-0.5 ,urn to 0.08-0.1 w. Such effects are probably due to both the stress-strained state of the

friction contact and the strength of the adhesive bond increasing

with film thickness. Decrease in the adhesive bond strength is

connected with a reduction in the area of contact caused by a loss

in both the elasticity and flexibility of the film as a whole. The

stronger bond between the contacting surfaces combined with a de-

crease in the film thickness also favours an increase in the fric-

tion coefficient. The minimum value of the friction coefficient

can be plotted vs. polymer film thickness; it decreases to about

0.45 for a PTFE-PP system (ref. 232).

The tribological properties of PE-PE systems are interesting

(refs. 185, 234-2361. The effect of the density of PE on the fric-

tion coefficient is pronounced. The friction coefficient of LDPE-

-LDPE systems (low density PE: density below 0.93 mg/m3), operat-

ing at low contact pressure (and high sliding speed) can reach 1.2

but decreases rapidly to as low as 0.05 with increase in contact

pressure and decrease in sliding speed (refs. 234, 235, 236). For

HDPE-IIDPE systems (high density, over 0.94 mg/mm3) , the friction coefficient is below 0.4 (refs. 185, 234), falling (hyperbolically

decreasing) to 0.1 when the density of the material is 0.965 n-g/m3




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tor change. The friction force vector is rotated and the angle of

the rotation at which disruption of the frictional bonds occurs

and the friction force becomes zero is determined by the ratio of

the shear and also depends on the ratio of the sliding (v) and vi-

brational (vv) speeds. With increase in the vv/v ratio the fric-

tional work rapidly increases (Fig. 10.2; ref. 868).

r Y - Load,N - Amplitude, pm 5 1b 1'5 2'0 $5 30 I c Frequency, kHZ 15 $0 46

'2 '4 '6 '8 ib

F ig . 10.2. F r i c t i o n a l work a t i n t r o d u c t i o n o f u l t r a s o n i c v i b r a t i o n s , pe rpend icu la r t o f r i c - t i o n p lane : W f Q - f r i . c t l o n a l work i n u l t r a s o n i c s f i e l d , W f - f r i c t i o n a l work. 1 - vv/v (vv - v i - b r a t i o n a l speed, v - s l i d i n g speed), 2 - f r e - quency, 3 - ampl i tude, 4 - s t a t i c normal load .

External vibrations perpendicular to the friction plane reduce

the friction force. The reduction is at a minimum when the vibrational overload is arround 1. Small vibrational overloads with low

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TABLE 3.6

SPECIAL INSTRUMENT OILS FOR LUBRICATION OF POLYMERIC MINIATURE SYSTEMS

OIL K 7132 K 7132 K 2363 K 2363 K 4563 9015 9024 9027 21000 2400 mv 10000

MOEBIUS ET FILS, ALLSCHWIL 1 (SWITZERLAND) MANUFACTURER I O r . TlLLWlCH GmbH, HORB-AHLDORF (F.R.G.) PROPERT I E S 4200 2400 1500

-6 2 -40 120 21

0.31

1

2 V i s c o s i t y , mm / s , OOC

20oc 625 1450 7600 150 266 1040 31 45 130

( a t 5OoC) -40 -40 -20 - 29 -18 -7 70 90 80 33.8 34.8 35.5

a t 1OOOC, 5 days 0 . 5 0.4

2 1 1.'" I 2 ( a f t e r 12 days)

I 4OoC Pour p o i n t , OC A p p l i c a t i o n temperature range, OC

Surface tens ion , mN/m

Evapora t ion ra te , % Ageing r e s i s t a n c e (Baader's t e s t D I N 51554), %

1250 434 123

(50C) -44 -40 200

49776 820 24000 10328 510 20700 4890 350 14100

- 26 -33 -4 1 -20 -30 - 27 200 120 120

28 20.6 20.9 a t 1050C. 16h

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l o a d s and t h a t w i t h a l a r g e amount of g r a p h i t e i s b e s t s u i t e d t o

h i g h s l i d i n g speeds and s m a l l l o a d s . M a t e r i a l s c o n t a i n i n g l e a d can

work w i t h o r w i t h o u t oil. Bronzes o r b ronze -g raph i t e material can

be g r e a t l y improved by add ing t i t a n i u m , n i c k e l , l e a d , z i n c , c o b a l t ,

i r o n o r aluminium. Bronze -g raph i t e w i t h 9.5-10.58 l e a d , 1.75% graph-

i t e , 1% i r o n and 0.5-1.5% o t h e r a d d i t i o n s i s a v e r y good b e a r i n g

m a t e r i a l ( r e f . 1 2 ) . S i n t e r e d b r a s s e s are r a r e l y used . They are man-

u f a c t u r e d u s i n g powders c o n t a i n i n g 10-50% z i n c . I n some cases 1 . 5 %

l e a d and 0.25-0.8% phosphorus a r e i n t r o d u c e d . Such materials have a

h i g h e r p l a s t i c i t y and b e t t e r w o r k a b i l i t y .

Nickel- and coba l t -based s i n t e r e d m a t e r i a l s are s u i t a b l e f o r

e l emen t s o p e r a t i n g under extreme c o n d i t i o n s . Nickel-based a l l o y s

c o n t a i n i n g i r o n or copper are v e r y c o r r o s i o n - r e s i s t a n t . N i c k e l w i t h

30% copper , c a l l e d monel, i s c o r r o s i o n - r e s i s t a n t i n a l k a l i s , water,

a 15% s o l u t i o n o f H C 1 and H C 1 s a l t s . I r o n - n i c k e l a l l o y s c o n t a i n i n g

50% o r more n i c k e l are s u f f i c i e n t l y c o r r o s i o n - r e s i s t a n t i n seawater

( r e f . 1 3 ) , a l k a l i s and some a c i d s o l u t i o n s . Nickel-based s i n t e r e d

materials a l s o c o n t a i n , a p a r t from g r a p h i t e , b e r y l l i u m , bo ron ,

molybdenum, S i c , B 4 C , T i c , WC, MoB2, Z r B 2 .

Cobalt-based s i n t e r e d materials show a d e c r e a s e i n t h e f r i c t i o n

c o e f f i c i e n t w i t h i n c r e a s e i n tgllperriture. The a l l o y i s s t r e n g t h e n e d by

i n t r o d u c i n g 5 - 1 % Pd and 3-7% T i c o r 5-20% Ag ( r e f . 1 2 ) .

The importance of n i c k e l , c o b a l t and t h e i r a l l o y s as a n t i - f r i c -

t i o n materials f o r long t e r m u s e a t h i g h e r t e m p e r a t u r e s is due t o

t h e i r ha rdness (HRC 52-58) . The coba l t -based materials can r u b

a g a i n s t s t a i n l e s s and m i l d steels.

Aluminium-based s i n t e r e d m a t e r i a l s a r e c h a r a c t e r i z e d by t h e i r

low s p e c i f i c w e i g h t , low c o s t and c o r r o s i o n r e s i s t a n c e . The compo-

s i t i o n o f some aluminium-based s i n t e r e d m a t e r i a l s i s g i v e n i n Ta-

b l e 2.5 ( r e f . 1 2 ) . Copper a d d i t i o n a l l o w s aluminium-based s i n t e r e d

materials w i t h l a r g e p o r e s t o be made. Mg and N i improve t h e m e -

c h a n i c a l r e s i s t a n c e of t h e a l l o y . 0.1-0.5% S i and 4 % Sn i n c r e a s e

t h e wear r e s i s t a n c e of Al-based mater ia ls . The a d d i t i o n of 0 . 1 - 5 . 0 %

Mg improves t h e a n t i - f r i c t i o n a l p r o p e r t i e s of aluminium-based

s i n t e r e d m a t e r i a l s . Al-based s i n t c r e d m a t e r i a l s c o n t a i n i n g Cu or Mg

a r e s u i t a b l e f o r t h e manufac tu re o f b e a r i n g e l emen t s working a t low

s p e c i f i c l o a d s . Al-based s i n t e r e d m a t e r i a l s impregnated w i t h s o l i d

l u b r i c a n t s such as MoS2 a r e used f o r t h e manufacture of b e a r i n g

elements which rub i n a vacuum or i n a i r w i t h o u t l u b r i c a t i o n . The

w e a r , t he rma l and c o r r o s i o n r e s i s t a n c e of Al-based s i n t e r e d m a t e r i -

a l s c o n t a i n i n g Mn, Mg, S i , Cu, C r , N i and Fe can be improved by t h e






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5 32

4 65

466

4 67

468

469

4 7 0

4 7 1

4 7 2

47 3

474

4 75

476

477

478

479

4 80

4 8 1

482

Ti l lw ich M.:Probleme d e r Kunststoffschmierung, i n : A c t e s de 10e Congres I n t e r n a t i o n a l de C h r o n o m e t r i e , Genbve 1979 , Socie t6 Suisse de Chronometrie, Geneve 1979, Vol. 3, p. 419. Shevchenko A . A . , e t a l . : W e t t a b i l i t y and creeping of polymers, i n : M e h a n o k h i m i c h e s k y e S v o y s t v a K o n s t r u k t i o n n y c h P o l i m e r n y c h M a t e r i a l o v p r i E k s p l o a t a c i v R a z l i c h n y h Sredah - T e z i s y D o k l a d o v , Lvov 1972 , i n Russian. S t eh r W . : Etsyntha - spez ia luh rena l f u r Kuns tof f lager . D i e Uhr ( 1 9 7 6 ) 7, 106. Schonhorn, e t a l . : Surface modi f ica t ion of polymers and prac- t i c a l adhesion. P o l y m e r E n g i n e e r i n g and S c i e n c e 1 7 ( 1 9 7 7 ) 7, 440.

CHAPTER 7 BBhm G . : Oberflkhenschuteverfahren und i h r Einsa tz i n d e r Werkstoff- und Tr ibotechnik , T. 1 and 2. Z e i t s c h r i f t f c r W e r k s t o f f t e c h n i k 1 5 ( 1 9 8 4 ) 3 and 4, pp. 9 4 and 124 . Montes H . , e t a l . : T r ibo log iza l behaviour of a t h i n Fe-Mo-S f i lm . Wear 9 2 ( 1 9 8 3 ) 2, 1 6 3 . Grigor iev I.Y. : L i f e i n v e s t i g a t i o n of a n t i - f r i c t i o n coa t ings a t o s c i l l a t i n g , s l i d i n g i n vacuum. T r e n i e i l z n o s 4 ( 1 9 8 3 ) 6, 120, i n Russian. Buck V . : P repa ra t ion and p r o p e r t i e s of d i f f e r e n t t ypes of spu t t e red MoS2 f i lms . Wear 1 1 4 ( 1 9 8 7 ) 3, 263. Fle ischauer P.D.: E f f e c t s of c r y s t a l l i n e o r i e n t a t i o n on environmental s t a b i l i t y and l u b r i c a t i o n p r o p e r t i e s of s p u t t e r e d MoS2 t h i n f i lms . A S L E T r a n s a c t i o n s 27 ( 1 9 8 4 ) 1, 82 . Nozenkov M.V., Semenov A . P . : A n t i f r i c t i o n c o a t i n g s based on molybdenum d i su lph ide wi thout bonding mater ia l , i n : T r e n i e ,

I znos i Smazochnye Mate r i a 1 y - Proceedings of t h e i n t e r n a t i o n - a l Conference i n Tashkent, 22-26 May 1 9 8 5 . Nauchnyi Sov ie t AN S.S.S.R. PO T r e n i i i Smazkam, Moscow 1985 , V o l . 2, p. 223, i n Russian. Gamulya G . D . , Lebedeva I . D . : Lubr ica t ing a c t i o n of lamellar s o l i d l u b r i c a n t c o a t i n g s under f r i c t i o n i n vacuum, i n : T r e n i e , l z n o s i Smazochnye M a t e r i a l y - Proceedings of t h e I n t e r n a t i o n - a l Conference i n Tashkent, 22-26 May 1 9 8 5 . Nauchnyi Sov ie t AN S.S.S.R. PO T r e n i i i Smazkam, Moscow 1985 , V o l . 2, p. 83 , i n Russian. Gamulya G . D . , et a l . : General r e g u l a r i t i e s of wear i n vacuum or s o l i d f i l m l u b r i c a n t s formulated wi th lamellar materials. Wear 93 ( 1 9 8 4 ) 3, 3 1 9 . Gamulya G.D. , et a l . : E f f e c t of running-in on endurance l i f e of a n t i - f r i c t i o n s o l i d l u b r i c a n t s c o a t i n g s i n vacuum. Ves t n i k M a s h i n o s t r o y e n i a ( 1 9 8 4 ) 11, 34, i n Russian. Sachek B.Y. , Skvortzov V.N. : Kine t i c of changing i n microhardness of s o l i d l u b r i c a n t coa t ings wi th MoS2 dur ing running- - in . TrenCe i l z n o s 5 ( 1 9 8 4 ) 6, 1124 , i n Russian. Fusaro R.L.: E f f ec t of s u b s t r a t e s u r f a c e f i n i s h on t h e l u b r i - c a t i o n and f a i l u r e mechanisms of molybdenum d i s u l f i d e f i lms . A S L E T r a n s a c t i o n 25 ( 1 9 8 2 ) 2, 111. Nosov M. I. : I n v e s t i g a t i o n of l u b r i c a t i n g p r o p e r t i e s of molybdenum d i su lph ide , g r a p h i t e and phtalocyanine. Kh i mya i T e k h n o l o g y a T o p l i v i Mase l ( 1 9 7 2 ) 7, 47, i n Russian. Anapolski i A.B. , e t a l . : Se lec t ing and i n v e s t i g a t i o n of t h e un lubr i ca t ed p a i r f o r j o u r n a l bea r ings i n helium atmosphere. T r e n i e i l z n o s 4 ( 1 9 8 3 ) 5, 916, i n Russian. Gerkema J . : Lead t h i n f i l m l u b r i c a t i o n . Wear 1 0 2 ( 1 9 8 5 ) 3, 241.

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1 I I 1 I

0.1 0.2 0.3 0.4 0.5 Sliding speed , m / s

F ig . 5 .10. E f f e c t o f l u b r i c a t i o n on f r i c t i o n c o e f f i - c i e n t o f m i n i a t u r e s tee l -po lymer j o u r n a l bea r ing . Bear ing ho le d iameter 2 mm, bear ing bush l e n g t h 1 0 mm, d iamet ra l c lea rance 0.03-0.08 mm, c o n t a c t p ressure 0.0625 MPa, l u b r i c a t i o n by d i rne thy lpo l ys i l oxane w i t h v i s c o s i t y 300 mm2/s ( a t 20OC) . Do t ted 1 ines g i v e cha- r a c t e r i s t i c s o f l u b r i c a t e d bear ings . 1 - PA 6, 2 - PC, 3 - POM h .

The effect of lubrication on the wear of some steel-polymer bear-

ings is presented in Fig. 5.11. It can be seen that the wear re-

duction in PA bearings is higher than in POM bearings. The decrease

in wear is particularly high when the pv value increases (Fig.5.12).

The wear in lubricated steel-PA bearings is higher than in lubri-

cated steel-POM bearings. The increase in the wear rate of minia-

ture lubricated steel-polymer journal bearings is generally pro-

portional to the increase in pv value.



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398

g r e a t accuracy ( 0 . 0 2 pm) by means of s h i e l d i n g t h e r e f l e c t i o n . The

a rea of contac t i s kept p e r f e c t l y dark and photographed through

t h e microscope 6 . The s h u t t e r of t h e camera is snapped by m e a n s o f t h e r e l ay and p h o t o t r a n s i s t o r 11. I n t h i s way, even i f t h e number

of revolu t ions is changed, t h e same con tac t l i n e of t h e jou rna l is

recorded. The o i l is s t o r e d i n the l u b r i c a t i n g tank 8.

Fig. 8.74. Apparatus f o r s tudy ing breakdown o f l u b r i c a n t f i l m between j o u r n a l and bear- i ng . 1 - a x i s made o f brass, 2 - pr ism, 3 - a quarter-wave p l a t e , 4,s - p o l a r i z i n g p l a t e , 6 - microscope, 7 - centres, 8 - o i l tank, 9 - b e l t , 10 - lamp, 11 - p h o t o - t r a n s i s t o r ( r e f . 634) .

S tud ie s of miniature bear ings under s p e c i a l condi t ions (low o r

high temperatures I o r i n a con t ro l l ed environment) , r equ i r e special- l y designed apparatus ( r e f . 635) . A device f o r t e s t i n g t h e t r i b o -

l o g i c a l p r o p e r t i e s of miniature jou rna l bear ings a t low tempera-

t u re s i s depic ted i n Fig. 8.75. The j ou rna l 1 r o t a t e s on the ro l -

l i n g bear ings . The bear ing bush t o be t e s t e d 2 i s placed i n the

holder 3 and loaded v i a t h e cy l inde r 4 by t h e weights Q, and Q2.

The jou rna l is driven by t h e electric motor 7. The r o t a t i o n speed

i s measured using the tachogenerator 1 0 on t h e s c a l e 11. The ex-

tensometr ic system c o n s i s t s of t h e l e v e l 5 wi th the extensometer

1 2 , ampl i f i e r 13 and osc i l l o scope 1 4 .

OC, t o -12OOC. Liquid n i t rogen vapour is used a s t h e cool ing me-

The cool ing system enables the temperature t o be lowered below

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The a c c u r a t e d e t e r m i n a t i o n o f s u r f a c e t e m p e r a t u r e s i n t r i b o -

l o g i c a l p r o c e s s e s from r a d i a n c e measurements is a d i f f i c u l t t a s k

w i t h many p i t f a l l s and s o u r c e s o f errors. There are t h e e r r o r s as-

s o c i a t e d w i t h i n f r a r e d measurements i n g e n e r a l , w i t h t h e p re sence

o f t h e s a p p h i r e i n t h e aforementioned c a s e , and w i t h t h e s l i d i n g

c o n t a c t p r o c e s s i t s e l f . A l is t o f p o t e n t i a l problems and f a c t o r s

t o c o n s i d e r , t o g e t h e r w i t h a p p r o p r i a t e comments o r recommendations,

i s g iven i n r e f . 578.

Accurate measurements o f i n c r e a s e s i n s u r f a c e t e m p e r a t u r e are

v i t a l t o o u r unde r s t and ing o f m i n i a t u r e systems because t h e s e i n -

creases are l i k e l y t o p l a y an i m p o r t a n t r o l e n o t o n l y . i n t h e me-

chanisms o f f r i c t i o n and wear b u t a l s o i n t h e f a i l u r e of l u b r i c a n t

f i l m s and i n t h e fo rma t ion i n s i t u of p r o t e c t i v e f i l m s on s o l i d

s u r f a c e s (see Chapters 4 and 5).

8,5 , QUALITY OF LUBRICANTS A N D COATINGS a . 5 . 1 . INTRODUCTION

The e v a l u a t i o n of t h e l u b r i c a n t s and

EP I LAMES)

c o a t i n g s ( e p i l a m e s ) before,

du r ing and a f t e r o p e r a t i o n i n m i n i a t u r e systems i s v e r y i m p o r t a n t .

The e v a l u a t i o n o f t h e l u b r i c a n t p r o p e r t i e s b e f o r e u s e i s q u i t e

s imple because o f t h e r e l a t i v e l y l a r g e volume o f l u b r i c a n t available

f o r s t u d y . The d i f f i c u l t y arises i n t h e d e s i g n o f s i m u l a t o r s f o r

t h e i n v e s t i g a t i o n and p r e d i c t i o n o f l u b r i c a n t behav iour i n r e a l

t r i b o l o g i c a l systems.

To determine t h e q u a l i t y o f a l u b r i c a n t d u r i n g or a f t e r u se i n

a m i n i a t u r e system i s ve ry d i f f i c u l t due t o t h e ex t r eme ly s m a l l

amounts i nvo lved - a s l i t t l e as 10-7g f o r t h e l u b r i c a t i o n o f a m i n i a t u r e watch b e a r i n g . The i d e n t i f i c a t i o n o f t h e p h y s i c a l and

chemical p r o p e r t i e s o f used ( aged) l u b r i c a n t i n m i n i a t u r e systems

i s a problem which has n o t y e t been s a t i s f a c t o r i l y s o l v e d .

The a n a l y s i s of t h e q u a l i t y o f t h e c o a t i n g ( e p i l a m e s ) on a

microelement , e s p e c i a l l y i n i n d u s t r i a l c o n d i t i o n s ( m a s s production) , i s a l s o ve ry d i f f i c u l t . The q u a l i t y o f t h e ep i l ame s i g n i f i c a n t l y

a f f e c t s t h e d u r a b i l i t y of rubb ing elements and t h e e f f i c i e n c y o f

l u b r i c a n t s .


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360

I F F- I-

Fig. 8.48. Test vessel f o r determining evapo- r a t i o n r a t e o f instrument o i l s . A - sphere, B - s p i r a l ( w i t h rod a t the end) t o ensure be t te r mixing o f n i t rogen w i t h o i l , C , D , E - elements f o r prevention o f o i l foaming, F - out f low.





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0 1

The b e a r i n g s w i t h POM b e a r i n g bushes demonst ra te b e t t e r wear

r e s i s t a n c e than PA 6 - based b e a r i n g s . A comparison of t h e r a d i a l wear rates f o r POM - and PA - based b e a r i n g s (based on t h e s t u d i e s d e s c r i b e d i n r e f . 1 7 4 ) is presented i n F i g . 4 . 7 .

1 I I *

I 2 3

F i g . 4 . 7 . Radial wear r a t e v s . contact pressure f o r steel -polymer m i n i a t u r e j o u r n a l bear ings. Nominal diameter 2.15 nun , e x t e r n a l diameter of t h e polymeric bear ing bush 6 mm, bear ing l e n g t h 2.1 mm, d i a m e t r a l c learance 1 .5-2%, s l i d i n g speed 0.0167 m / s , s l i d i n g d i s - tance 3 0 km. 1 - P A 6, 2 - P A 66, 3 - POM c , 4 - POM h .

I n c r e a s i n g t h e c o n t a c t p r e s s u r e r e s u l t s i n a n i n c r e a s e i n t h e radial

wear r a t e , p a r t i c u l a r l y f o r PA - based b e a r i n g s , b u t when t h e con- t a c t p r e s s u r e is high enough (above 2 MPa) t h e i n c r e a s e i n t h e

r a d i a l wear r a t e of POM - based b e a r i n g s i s a l s o s i g n i f i c a n t . I n c r e a s i n g t h e c o n t a c t p r e s s u r e above 3 MPa r e s u l t s i n a dramatically h igher wear r a t e ( r e f s . 1 6 8 , 1 7 0 ) . The e f f e c t of t h e s l i d i n g speed


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15

2 , 3 , M I N E R A L S , CERAMICS, COMPOSITES

These m a t e r i a l s are wide ly used because of t h e i r s p e c i a l t r i b o -

l o g i c a l p r o p e r t i e s , r e s i s t a n c e t o c o r r o s i o n and the rma l shock . Co-

rundum ( s a p p h i r e and ruby) - A 1 2 0 3 - i s o f t e n used. Some of t h e p r o p e r t i e s of s a p p h i r e and ruby a r e l i s t e d i n Tab le 2 .7 . The pro-

p e r t i e s of n a t u r a l and a r t i f i c i a l s t o n e s a r e p r a c t i c a l l y t h e same.

Ruby i s corundum t o which chromium o x i d e h a s been added t o make i t

r e d .

TABLE 2.7.

PROPERTIES OF CORUNDUM, AGATE AND SITALL

PROPERT I ES

Compos i t i on

3 Dens i t y , mg/mm Hardness, Mohs, MPa

E l a s t i c i t y modulus, MPa

Compressive s t r e n g t h , MPa

C o e f f i c i e n t f thermal ex-

D i e l e c t r i c cons tan t

Water absorp t ion , %

Chemical r e s i s t a n c e

pansion, 10- g /K

Compressive s t r e n g t h i n r a d i o a c t i v e water a t 5OO0C, MPa

CORUNDUM

A'23

3.9

9 (1.85-2.75)*10 4

(3.5-3.9) lo5 2.06 * l o 3

5-6.7 7.5-10

J

Res i s t a n t aga ins t ac ids 3nd NaOH. Non- r e s i s t a n t

3ga ins t HF s t 3 O O 0 C

17.65

AGATE

Si02 96.3-98.9 %

R 0 0.18-0.97 % 2 3

2.6

5.5-7 (0.9-1 .O) ' 1 0

(7.8-8.9) ' 10

(8.75-11 .9) * l o 2

4

4

1.4-1.38

i es i s t a n t agai n s t acids except HF. ' a r t i a l l y r e s i s - t a n t a g a i n s t NaOH

S ITALL

S i O z - 46%

A1203- 13

Fe203- 3 FeO - 9.2 CaO - 8.6

Cr203- 1.0 MgO - 7.0

R20 - 0.5

2.85

7.5 0.98- 1 D3

7.8.10

7.0-9.0

0.02

l es i s t a n t i g a i n s t s u l - > h u r i c a c i d (99.8%) and K 1 (99%)

Corundum is h i g h l y r e s i s t a n t t o chemica l a c t i o n even a t h i g h

t e m p e r a t u r e s and i n t h e p r e s e n c e of r a d i o a c t i v e water vapcur ( ref .7) .


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2 4 3

I n minia ture bear ings such a s watch j e w e l bear ings , which are

r e s i s t a n t t o dangerous r a d i a l i n e r t i a over loads of more than l o 4 g,

t h e t y p i c a l volume of t h e o i l depos i t is 10-2 -10-3 mm3. For such

bear ings t h e a n a l y s i s f o r nonspreading of an o i l is the re fo re super-

f luous .

6 , 4 , LUBRICANT DURABILITY

The ope ra t ing condi t ions of instrument l u b r i c a n t s a r e very se-

vere . They must provide e f f e c t i v e l u b r i c a t i o n of microbearings over

long per iods , o f t e n under very high s p e c i f i c l oads (up t o 2-3 GPa)

and impact loads . Other adverse f a c t o r s a r e high temperature v a r i -

a t i o n s , a c t i v i t y of t h e wear d e b r i s and rubbing element materials,

in f luence of t h e environment (oxygen , i n d u s t r i a l gases and impu- r i t i e s ) , humidity, and var ious types of r a d i a t i o n (W, r ad ioac t iv -

i t y , cosmic) . The l u b r i c a n t q u a n i t i e s appl ied f o r l i f e l u b r i c a t i o n

a r e very small . The l u b r i c a n t should t h e r e f o r e be nonspreading and

should demonstrate e x c e l l e n t l u b r i c i t y and high d u r a b i l i t y . By "dur-

a b i l i t y " w e mean t h e chemical and phys ica l s t a b i l i t y of a lubricant.

Generally speaking, f o r instrument l u b r i c a n t s , wi th an inc rease i n

t h e l u b r i c i t y and nonspreading p r o p e r t i e s , t h e d u r a b i l i t y decreases.

The chemical s t a b i l i t y can be es t imated v i a t h e de te rmina t ion

of t h e dynamics of ox ida t ion and polymerizat ion processes , which

r e f l e c t t h e ageing of t h e l u b r i c a n t . Ageing i s s t imu la t ed by t r i b o -

l o g i c a l and environmental e f f e c t s . An extreme ins t ance of ageing i s

t h e t o t a l coking of a l u b r i c a n t . The sum of va r ious e n e r g e t i c a l e f -

f e c t s ( t r i b o l o g i c a l and environmental) f o r t o t a l coking is a con-

s t a n t value ( r e f . 4 3 9 ) . The ox ida t ion and polymerizat ion processes

a r e not t h e only chemical changes i n instrument o i l s , High humidity

and temperature can provoke a hydro ly t i c r e a c t i o n i n s e v e r a l o i l s

( e .g . s y n t h e t i c o i l based on t r i c r e s y l phosphate) and t h e s e c r e t i o n

of co r ros ive agents .

A marked inc rease i n t h e v i s c o s i t y and dens i ty of oil occurs a s

a r e s u l t of t h e ox ida t ion and polymerizat ion processes . The su r face

tens ion of o i l decreases non-monotonically, t h e a c i d i t y and t h e

abso lu te r e f r a c t i v e indexes inc rease , t h e co lour of t h e o i l changes

and t h e o i l l o s e s i t s l u b r i c a t i n g p r o p e r t i e s . The speed of t h e age-

ing process depends s i g n i f i c a n t l y on t h e r e l a t i o n of t h e a rea of

con tac t with oxygen t o t h e t o t a l volume of t h e o i l depos i t .

The ageing dynamics of o i l a r e l imi t ed by t h e p r o p e r t l e s of t h e

o i l and t h e opera t ing condi t ions . O i l s of n a t u r a l o r i g i n , whether



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444

250

MO

fiuori noted synthetic oils dica microgel

- _ - - - Mineral oils t

DoLyurea thickener- - - - - - ,- - - _ _ - -

torque speeds

0 po ra t i ng co ndi I io n s

F i g . 9 . 2 0 . C r i t e r i a f o r s e l e c t i n g oi l s and greases f o r l u b r i c a t i o n o f miniature r o l l i n g bearings ( r e f s 674 and 6 7 6 ) .

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553

9 1 5

9 1 6

9 1 7

9 1 8

9 19

9 20

9 2 1

9 2 2

9 2 3

9 2 4

9 2 5

926

9 2 7

9 2 8

9 29

93 0

93 1

9 32

9 33

9 34

9 35

9 36

9 3 7

9 3 8

e d i t e d by W. J. Bar tz . Technische Akademie Ess l ingen 1 9 8 4 , paper 13 . Rymuza 2. : S e l f - l u b r i c a t i o n i n m i n i a t u r e m e t a l systems. Pomia - r y A u t o m a t y k a K o n t r o l a ( 1 9 8 7 ) 5, 113 , i n P o l i s h . Rymuza 2. : S e l f - l u b r i c a t i o n i n m i n i a t u r e polymer systems. P o m i a r y A u t o m a t y k a K o n t r o l a ( 1 9 8 7 ) 4, 86, i n P o l i s h . Burcan J . : Problems of p i v o t i n g f r i c t i o n i n e l a s t i c p o i n t contact . Z a g a d n i e n i a E k s p l o a t a c j i Maszyn ( 1 9 8 6 ) 1, 153, i n Polish. Holzhauer W. , e t a l . : S t a r t - s t o p e v a l u a t i o n s of hydrodynamic gas b e a r i n g m a t e r i a l s a t 296 K and 7 7 K. ASLE T r a n s a c t i o n s 28 ( 1 9 8 5 ) 4 , 415. Asada T. , e t a l . : Hydrodynamic b e a r i n g s f o r p o r t a b l e VTR head assemblies . N a t i o n a l T e c h n i c a l R e p o r t 3 1 ( 1 9 8 5 ) 6, 854, i n Japanese. I b a G . : G a s b e a r i n g . J u n k a t s u - J o u r n a l o f Japan S o c i e t y o f L u b r i c a t i o n E n g i n e e r s 30 ( 1 9 8 5 ) 8, 577 , i n Japanese. Buschow K . H . J. : New permanent magnet materials. M a t e r i a l s S c i e n c e R e p o r t s 1 ( 1 9 8 6 ) 1, 1. C a r l i s l e B.H. : Neodymium chal lenges f e r r i t e magnets. M a c h i n e D e s i g n 5 8 ( 1 9 8 6 ) 1, 24. Rymuza 2. : Minia ture permanent magnet b e a r i n g s . P o m i a r y A u t o - m a t y k a K o n t r o l a (19881 , 4, 163 , i n P o l i s h . Rymuza 2.: C a p i l l a r y b e a r i n g s . P o m i a r y A u t o m a t y k a K o n t r o l a ( 1 9 8 8 ) , 6, 129, i n P o l i s h . Chappuis J.: L u b r i c a t i o n by a new p r i n c i p l e : t h e u s e of non- -wet t ing l i q u i d s . Wear 77 ( 1 9 8 2 ) 3, 303. Demian T. , Pascu A. : I n v e s t i g a t i o n and c a l c u l a t i o n of c a p i l - l a r y b e a r i n g s . C o n s t r u c f i a de M a g i n i 3 8 ( 1 9 8 6 ) 1, 21, i n Rumanian. Rymuza 2. : Polymeric j o i n t s i n f i n e mechanisms. P o m i a r y A u t o - m a t y k a K o n t r o l a ( 1 9 8 7 ) 12, 2 7 9 , i n P o l i s h . Watkinson K . : S n a p - f i t j o i n t s i n p l a s t i c s . E n g i n e e r i n g ( 1 9 8 4 ) 1 0 , 734 . Weissmantel H. , .: Filmgelenke z u r F u n k t i o n s i n t e g r a t i o n b e i Kunststoffter?E:.LFeinwerktechnik + Messtechnik 93 (1985) 2, 89. Schmidt H . : Filmgelenke aus verstkirktem Polypropylen und aus Aceta lcopolymer isa t . P l a s t v e r a r b e i t e r 3 4 ( 1 9 8 3 ) 9, 774 . Schalz K . J . : Hochgenaue Schlag- und Reibmomentmessung sowie selbstaus- r ichtendes Klebeverfahren zur Qual i tStsste igerung von PrZzisions-Kugel- lagerungen. N o . 1 4 7 i n series : KonstruktionstechnikrNaschinen-

elemente. V D I Verlag, Diisseldorf 1 9 8 6 . Bankmann G. : Lagerung von S c h r i t t m o t o r e n f c r Datenspe icher . F e i n w e r k t e c h n i k + M e s s t e c h n i k 9 4 ( 1 9 8 6 ) 2, 79. Graham E.E. , Klaus E.E. : L u b r i c a t i o n from t h e vapour phase a t high tempera tures . A S L E T r a n s a c t i o n s 29 ( 1 9 8 6 ) 2, 229. Komatsuzaki S. , e t a l . : Bearing damage by e lec t r ica l wear and i t s e f f e c t on d e t e r i o r a t i o n of l u b r i c a t i n g g r e a s e . L u b r i c a t i o n E n g i n e e r i n g 4 3 ( 1 9 8 7 ) 1, 25. C a r r d D. J. : P e r f l u o r o p o l y a l k y l e t h e r oil degrada t ion: i n f l u e n c e of FeF3 formation on steel s u r f a c e s under boundary c o n d i t i o n s . A S L E T r a n s a c t i o n s 29 ( 1 9 8 6 ) 2, 121. Tomaru M . , e t al.: Grease-life e s t i m a t i o n and g r e a s e d e t e r i o - r a t i o n i n s e a l e d b a l l b e a r i n g s , i n : P r o c e e d i n g s o f t h e JSLE i n t e r n a t i o n a l T r i b o l o g y C o n f e r e n c e , Tokyo, Japan, 8-10 J u l y 1985 , e d i t e d by Y. T a m a i . E l s e v i e r , Amsterdam 1985 , Vol. 3, p. 1039. Dzyuba V . I . , Podmastereev K . U . : Eva lua t ion of l u b r i c a t i n g f i l m i n r o l l i n g b e a r i n g s . V e s t n i k M a s h i n o s t r o y e n i a ( 1 9 8 6 ) 5, 8, i n Russian . Rymuza 2.: S e l f - l u b r i c a t i o n i n m i n i a t u r e systems by t r a n s f e r of s o l i d l u b r i c a n t . P o m i a r y A u t o m a t y k a K o n t r o l a ( 1 9 8 6 ) 7, 168 ,

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3,4, SOLID LUBRICANTS

S o l i d l u b r i c a n t s a r e more and more f r e q u e n t l y used s i n c e t h e y

are ve ry good l u b r i c a n t s f o r t r i b o l o g i c a l systems o p e r a t i n g under

extreme c o n d i t i o n s : low and h i g h t e m p e r a t u r e s , vacuum, r a d i a t i o n ,

c o r r o s i v e environment , h i g h c o n t a c t p r e s s u r e s , h i g h f r equencyosc i l -

l a t i n g motion, o r s t a r t - s t o p ( i n t e r m i t t e n t ) motion (e .g . i n gas

b e a r i n g s ) . The most w ide ly used s o l i d l u b r i c a n t s are i n o r g a n i c sub-

s t a n c e s : g r a p h i t e and molybdenum d i s u l p h i d e . The good l u b r i c a t i n g

p r o p e r t i e s of g r a p h i t e are due t o t h e l a y e r e d l a t t i c e s t r u c t u r e and

a l s o depend on adsorbed f i l m s , i n p a r t i c u l a r of water vapour , which

p rov ide s u r f a c e s w i t h low adhes ion . The u s e o f g r a p h i t e is t h e r e -

f o r e e f f e c t i v e i n a humid atmosphere; i n a vacuum it loses its anti-

- f r i c t i o n p r o p e r t i e s . A t t empera tu res o v e r 45OoC it forms carbon

d i o x i d e . When s u i t a b l e o x i d e l a y e r s a r e p r e s e n t g r a p h i t e keeps i t s

l u b r i c a t i n g p r o p e r t i e s up t o 60OoC. Mix tu res o f g r a p h i t e w i t h m e t a l

o x i d e s (such as PbO) o r me ta l s a l t s adhe re t o m e t a l s u r f a c e s and

reduce f r i c t i o n c o n s i d e r a b l y ( r e f . 6 2 ) . The f r i c t i o n c o e f f i c i e n t o f

g r a p h i t e i n a normal atmosphere i s abou t 0 .2 ( r e f . 117). G r a p h i t e

i s a good l u b r i c a n t a t room t empera tu re and a t 5OO0C b u t n o t a t

i n t e r m e d i a t e t empera tu res ; a t room t e m p e r a t u r e , env i ronmen ta l con-

t aminan t s s e p a r a t e g r a p h i t e l a m e l l a e and t h e y d e s o r b a t h i g h e r t e m -

p e r a t u r e s , and a t t empera tu res above 500C, as mentioned b e f o r e ,

ox ides a i d i n t h e l u b r i c a t i o n p r o c e s s ( r e f . 1 1 7 ) .

Molybdenum d i s u l p h i d e (MoS2) h a s a lamellar s t r u c t u r e and

c r y s t a l l i z e s i n t h e hexagonal system w i t h t r i g o n a l symmetry. The

s u l p h u r l a y e r s forming t h e s u r f a c e of t h e MoSZ c r y s t a l g i v e s t r o n g

adhes ion t o me ta l s u r f a c e s . The f r i c t i o n c o e f f i c i e n t o f MoS2 can be

very low (less than 0 . 2 ) , e s p e c i a l l y when v e r y h igh c o n t a c t p r e s - s u r e i s a p p l i e d , a l though i n t h e p re sence o f water t h e f r i c t i o n

c o e f f i c i e n t and wear i n c r e a s e . Unlike g r a p h i t e , MoS2 is a good

l u b r i c a n t i n a h igh vacuum, demons t r a t ing ve ry low f r i c t i o n coe f -

f i c i e n t (below 0 . 0 5 ) . A t empera tu re i n c r e a s e from 20 t o 100C re-

duces t h e f r i c t i o n c o e f f i c i e n t s i n c e env i ronmen ta l contaminants are

d e t r i m e n t a l t o l u b r i c a t i n g e f f e c t i v e n e s s . Above 100C, t h e f r i c t i o n

c o e f f i c i e n t remains r e l a t i v e l y s t a b l e u n t i l s e v e r e o x i d a t i o n of

MoS2 o c c u r s above 37OoC. The s m a l l e r t h e p a r t i c l e s of MoS2 are , t h e

h i g h e r t h e o x i d a t i o n ra te w i l l b e .

G r a p h i t e and MoS2 o r i e n t r a p i d l y when rubbed because o f t h e

c r y s t a l s t r u c t u r e . The b a s a l p l a n e s become p a r a l l e l t o t h e f r i c t i o n

s u r f a c e which f a c i l i t a t e s e a s y s h e a r . Powder b l e n d s o f high-grade

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4 99

with a viscosity of 8 2 mPa s at 37OC gives a remarkable reduction

in the wear rate of all-metal prostheses and in friction of metal-

UHMWPE joints (a shoulder joint prosthesis was used for the ex-

periments; ref. 850) . Elastohydrodynamic lubrication of artificial hip joints is very

effective; fluid lubricating film can be achieved even with the low

viscosity synovial fluid (refs. 991, 9 9 2 ) . The coefficient of fric-

tion in prototype artificial hip joints which have compliant surface

lining ( 2 mm thick, a hardness of about 4 MPa) lubricated with the

low viscosity synovial fluid present in diseased joints after sur-

gery is remarkably low and comparable with normal healthy human

joints (ref. 9 9 2 ) .

Marked variations in the coefficient of friction for the slid-

ing of bovine articular cartilage and UHMWPE against surgical grade

steel (EN 58J), glass or cartilage in the presence of synovial

fluid, saline solution or distilled water when interfacial electric-

al potentials were applied were observed (ref. 9 9 3 ) . Such friction-

al variations were dependent upon the lubricant present, the rub-

bing materials and the test conditions.

The failure of joint prostheses is mainly due to the effects

of loosening and fracture, but in order to increase the lifetime

of the prosthesis attention must be paid to all possible causes of

failure (e.g. wear) (ref. 11). The new improved encapsulated total

joint replacements, or the new designs of cups with large rims, and

improvements in surgical techniques play an important part in ef-

forts to prevent acrylic cement particles from getting into the

friction area and in efforts to reduce wear by artificial lubrica-

tion (for a review of papers on the mechanical properties of acrylic

cement see ref. 851). The use of cement-less prostheses such as the

alumina-alumina hip joint prosthesis is also an effective solution

to these problems of prosthesis failure.

Prosthetic heart valves are immersed in the blood. Presently

about 4 0 types of artificial valves are used. Ball and disk valves

are most often applied. The valve must be durable since a life ex-

pectancy of a least 25-30 years is desirable (heart valves cycle

at approximately 4 2 million times a year). Materials used in the

valve must be compatible with tissue and blood i.e. must not be

corroded or initiate clots, they must have a density close to that

of blood, and they must be able to withstand common hospitalsteri-

lization techniques. Materials currently used for valve cages in-

clude titanium (having a relatively small density), Co-Cr-Mo alloy

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402

t o determine t h e ox ida t ive s t a b i l i t y of l u b r i c a n t s by use of a

simple e l e c t r o n i c (semiconductor) gas senso r which responds t o

gaseous oxida t ion products . A sensor such as t h e FIGARO model 2 0 2 ,

s i m i l a r t o t hose used t o d e t e c t a combustible atmosphere , responds equa l ly w e l l t o deu te ra t ed and non-deuterated l u b r i c a n t s and has

been success fu l ly used t o monitor l u b r i c a t i o n systems inc lud ing

s y n t h e t i c hydrocarbons , azelate esters , and p e n t a e r y t h r i t o l t e t ra - esters ( r e f s . 6 3 9 , 8 9 3 ) .

12

Fig. 8.77. Device f o r determining darking or ageing grade o f lubr icant . 1 - l i g h t source, 2 - lubr icant sample, 3 - con- denser, 4 - f i l t e r , 5 - photoelement, 6 - system f o r compensation o f non-balancing vol tage, 7 - logarithmic a m p l i f i e r , 8 - system compensating p o l a r i z i n g current o f logar i thmic a m p l i f i e r , 9 - d i f f e r e n t i a l a m p l i f i e r , 10 - system of c o n t r o l l e d v a r i a b l e , 1 1 - a m p l i f i c a t i o n corrector , 12 - l i n e a r i n d i c a t o r .

The t r i b o l o g i c a l processes such as material t r a n s f e r , k i n e t i c s of t h e f r i c t i o n and wear, etc. i n unlubr ica ted and lubricated sys-

t e m s can be success fu l ly s t u d i e d by use of t h e a forement ionedteh-

niques (Chapters 6 . 2 . 6 , 8.5.4 , 8.5.5 , 8 . 6 ) . The techniques for


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221

ed . The polymer c o a t i n g s on me ta l s u b s t r a t e s were u n a f f e c t e d by

even t h o s e p o l a r o r g a n i c o i l s which had some a d v e r s e e f f e c t s on t h e

same c o a t i n g s on r e s i n o u s s u r f a c e s , emphasizing t h e i n f l u e n c e o f

t h e unde r ly ing s u r f a c e . The a d h e s i v e q u a l i t i e s o f t h e f i l m s f o r any

o f t h e pane l s o r m e t a l l i c s u r f a c e s t e s t e d were n o t a f f e c t e d by ex-

posu re t o an environment o f 1 0 0 % R.H. and 49OC f o r one week.

These i n v e s t i g a t i o n s ( r e f s . 402,403) i n t o t h e p r e v e n t i o n o f o i l

sp read ing (Stop-Oil method) showed that for m e t a l and m i n e r a l s u r f a c e s

t h e two polymers i n v e s t i g a t e d were very good. I f d u r i n g normal u s e

t h e in s t rumen t w i l l b e s u b j e c t e d t o a b r u p t t e m p e r a t u r e changes from

subze ro t o h i g h t e m p e r a t u r e i n c o n d i t i o n s o f h i g h humidi ty cond i -

t i o n s , t h e PFOSEA c o a t i n g shou ld b e p r e f e r r e d because t h i s p l y e s t e r

w i t h s t a n d s such c o n d i t i o n s ; o t h e r w i s e PFOMA shou ld be used .

The PFOMA c o a t i n g ( 2 % PFOMA s o l u t i o n i n hexa f luo roxy lene ) h a s

been t e s t e d and used f o r t h e p r e v e n t i o n o f l u b r i c a n t m i g r a t i o n from

t h e b a l l b e a r i n g s of servo-motors ( r e f . 4 0 5 ) . A v a r i e t y of l u b r i -

c a n t t y p e s w e r e c o n s i d e r e d : s i l i c o n e s , d i e s t e r s , s i l i c o n e - d i e s t e r

b l e n d s , g r e a s e s , soap-thickened d i e s t e r s , soap-thickened s i l i c o n e -

- d i e s t e r b l e n d s ( a l l d i e s t e r l u b r i c a n t s c o n t a i n e d 0 . 5 % a n t i o x i d a n t

and 2 . 0 % r u s t i n h i b i t o r ) . The l i q u i d l u b r i c a n t s ranged i n v i s c o s i t y

from 1 0 0 0 t o 4 2 0 0 0 nun2/, a t -53.9OC. B a r r i e r f i l m s of PFOMA less

t h a n 1,um t h i c k were depos ted on t h e fo rehead s u r f a c e s o f t h e b a l l -

-bea r ing r i n g s . These i n v e s t i g a t i o n s showed t h a t PFOMA c o a t i n g s are

ve ry e f f e c t i v e i n p r e v e n t i n g t h e l u b r i c a n t from s p r e a d i n g . Bea r ings

t r e a t e d w i t h such a b a r r i e r have i n c r e a s e d t h e l i v e s o f serw-motors

from 300 t o n e a r l y 4000 h o u r s .

A PFOMA c o a t i n g can b e a c c i d e n t a l l y formed on t h e rubb ing s u r -

f a c e s of t h e b a l l b e a r i n g s . When t h e y become worn, t h e traces of

PFOMA may r e s u l t i n d r y rubb ing o f metal- to-metal s u r f a c e s . I f t h e

l u b r i c a n t does n o t q u i c k l y come between t h e rubb ing s u r f a c e s , sei-

z u r e is p o s s i b l e . I n h i s i n v e s t i g a t i o n s i n t o gyroscope b e a r i n g s ,

Ahlborn ( r e f . 4 0 6 ) showed t h a t when t h e s l i d i n g speed o f t h e b a l l

i s less t h a n 1 . 0 7 m / s and t h e r e a l i s t i c s p e c i f i c l o a d s ( 8 0 0 MPa,

p r a c t i c a l l y no s e i z u r e s o c c u r . S e i z u r e i s p o s s i b l e o n l y when t h e

v i s c o s i t y of t h e l u b r i c a n t i s t o o h i g h and t h e o i l cannot q u i c k l y

come between t h e m e t a l l i c s u r f a c e s a f t e r t h e d e s t r u c t i o n o f t h e

PFOMA l a y e r and when t h e h e a t i n g i n t h e rubb ing r e g i o n i s very high.

S e l e c t i n g t h e optimum s o l v e n t f o r t h e p r e p a r a t i o n o f b a r r i e r

epi lame f i l m s i s v e r y impor t an t . B e r n e t t ( r e f . 407) has i n v e s t i -

g a t e d t h e e f f e c t on PFObIA f i l m o f a l t e r n a t i v e s o l v e n t s f o r t y p i c a l

hexa f luo roxy lene (HFX) ( w i t h b o i l i n g p o i n t 116OC) . These w e r e :


0444874011/files/00205___02f8946e5bd54b4780bcd7e2ca16ddb3.pdf

This relationship can be approximated

I = a17(et,l)a18 il w,l

195

with the following formula:

(5.32)

* where IWI1 is the radial wear intensity in ,um/km, and etIl the ap-

parent stored frictional energy density (ASFED, see Chapter 4.2.1)

for lubricated bearings, measured in MJ/mm3, parameters a17 and

a18 are 106.6 and - 1.4866 respectively.

ings similar to the lubricated miniature steel-polymer journal

bearings analysed since eqn. (5.32) means that

The relationship (5.32) can be used to predict wear in bear-

a2 0 a19 IW,l = et,l (5.33)

where IwIl is the same as in eqn. (5.32), etll is the maximum den-

sity of the thermal energy stored in the polymeric material in

mJ/mm3 (see eqn. (4.19)), and parameters a19 and a20 are 23.12 and

0.3273 respectively.

The temperature rise in the friction area, which needs to be

known in order to determine etll, can be estimated using a formula

similar to that for unlubricated bearincjs (eqn. (4.21)). Since the

friction coefficient for lubricated bearings can be determined

from eqn. (5.27), by taking into consideration eqn. (4.4) the fol-

lowing formula can be used for estimating the temperature rise hT1

for lubricated bearings:

(5.34) - (a3v+a4)

AT^ = 1150 601 pv(alv+a2)p (1-0.12 p

For pI vI p , d, A , k and 6olsee eqns. (4.4), (4.21) and (5.27); the values of the parameters all

eqn. (4.4). The coefficient J01 for lubricated bearings, as found

in experiments on miniature steel-polymer journal bearings ((3 2.15

nun), can be taken for PA 6, PA 66, POM h and POM c bearings as

6,1 =0.06p'0'6 and for the bearings PA 6 + 25% glass fibre Sol = 0.08 p-0.5 (contact pressure p in MPa).

a2' a3 and a4 are given after

By combining eqns. (4.19), (5.32) and (5.34), the radial wear

intensity of lubricated miniature steel-polymer journal bearings

similar to those investigated can be estimated.

The radial wear rate of lubricated bearings as a function of

the sliding distance can be predicted in a similar way as for un-

lubricated bearings (see Chapter 4.2.1). The value of Cr (eqns.

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289

the surfaces occurs and the lubricating effect of the oxides re-

duces the friction coefficient and gives practically negligible

wear. At the limiting temperature, where oxidation is very strong

and the friction coefficient relatively low, the oxides spa11 and

the wear becomes high. During sliding in a vacuum (1.5 Pa)

the above effects do not occur; the friction coefficients increase

as a function of the temperature (to 0.9 for Tic-Ni at 7OO0C and

above 1.0 for Cr3C2-NiCr at 900OC). Because of strong adhesion be-

tween Ni bonding elements, Cr3C2-NiCr coatings can be applied in

radioactive environments.

WC and WC+Co coatings (15-55 ,um thick) deposited by electro-

phoresis and sintering on steels demonstrate high wear and thermal

resistance and have high density. They are used to coat the sur-

faces of measuring instruments, which are subject to wear. Cemented

carbide coatings a few micrometers thick, deposited by metallic

surface fusion (MSF) on elements of computer card machines, de-

monstrate high abrasive wear resistance when in contact with paper

(ref. 525). The so-called MSF process allows a molten overlay of

electrically conductive material to be applied to a metallic base.

Apart from cemented carbide, chromium,gold and other substance can

also be deposited by this method. Ferrous bases are usually clad,

but stainless steel and chromium substrates, as well as chromium-

-plated tungsten and molybdenum elements, may be treated. In prac-

tice, the best results are obtained when elements are dabbed with

a light oil before being treated. A good surface finish on the

substrate (Ra g 0.4 ,um) is essential.

Tungsten carbide can be deposited on nickel substrates by

carbide electrodeposition (ref. 526); tantalum has also been suc-

cessfully plated and other carbides (e.g. chromium carbide) can

also be deposited. This method can be used for plating complex

shapes.

Enameled oxide glazes (A1203 and other metal oxides) on steels

provide useful protection against the action of flowing agressive

media at elevated temperatures. Since such coatings are very thick

(minimum 0.1 nun) they are sensitive to impact and can split, espe-

cially at temperatures above 800-900C.

Conversion coatings are the effect to conversion of the metal

(All Ti, Tat W, Mot Hf, Zr) surface to metal oxide due to an anodic

process (anodizing) or the formation of insoluble phosphate crys-

tals on Fe, All Ti, Cu or galvanized steel surfaces (phosphatiz-

ing). Anodized coatings are extremely hard and have good abrasive

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1 1 2

When t h e j o u r n a l is made of POM h , t h e wear of b e a r i n g bushes

made of PA 6 6 o r PBTP r e i n f o r c e d w i t h g l a s s f i b r e o r g l a s s micro-

beads i s d i f f e r e n t ( r e f . 1 8 9 ) . The wear ra te of a bush made of

PA 66 + 3 0 % (by weight) g l a s s f i b r e ( l e n g t h 0.3-0.8 mm, d iameter 0 . 1 5 mm) a f t e r a s l i d i n g d i s t a n c e of 20 km i s s i g n i f i c a n t l y lower

t h a n t h e wear of a b e a r i n g bush made of PA 6 6 + 2 8 % g l a s s microbeads (d iameter 5-50 ,um) ( F i g . 4 . 2 2 , based on r e f . 1 8 9 ) .

Sliding distance, km

F i g . 4.22. Rad ia l wear o f bea r ing bush o f POM h ( j o u r n a l ) r e i n f o r c e d polymer j o u r n a l bea r ing vs . s l i d i n g d i s t a n c e . Bear ing h o l e diameter 2.7 mm, bear ing l e n g t h 1 mm, r e l a t i v e c lea rance 4-6%, s l i d i n g speed 0 . 0 1 3 1 m / s , c o n t a c t p ressure 1 . 5 MPa. 1 - PBTP + 28% g lass microbeads, 2 - PBTP + 30% g l a s s f i b r e , 3 - PA 66 + 28% g l a s s microbeads, 4 - PA 66 + 30% g l a s s f i b r e .

The volume wear of t h e POM h j o u r n a l i n t h e s e b e a r i n g s a f t e r a

s l i d i n g d i s t a n c e of 1 0 , 20 and 30 km i n POM h-PBTP + 30% g l a s s



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189

of polymers. The problems of t h e l u b r i c a t i o n of polymeric sys t ems

w i l l b e d i s c u s s e d i n Chapter 6 .6 . S p e c i a l i n s t r u m e n t o i l s which

can be used f o r t h e l u b r i c a t i o n of m i n i a t u r e polymeric sys t ems are

d e s c r i b e d i n Chap te r 3 . 2 .

The wear of l u b r i c a t e d m i n i a t u r e steel-polym.er j o u r n a l bea r -

i n g s ( u s u a l l y l u b r i c a t e d w i t h one d rop of o i l ) i s t h e e f f e c t of

adhes ive -cohes ive i n t e r a c t i o n s on t h e i n t e r f a c e ( i f t h e the rma l

e f f e c t s can be n e g l e c t e d , i . e . t h e t e m p e r a t u r e rise i n t h e f r i c -

t i o n a r e a A T < 3 K ; see F i g . 5 . 2 2 ) . The volume o f t h e po lymer i c ma-

t e r i a l worn, V l , can t h e r e f o r e be found u s i n g t h e f o l l o w i n g f o r -

mula, s i m i l a r t o eqn. ( 4 . 7 ) ( r e f . 1 9 6 ) :

(5 .19)

The l u b r i c a t e d wear can be determined f o r b e a r i n g s o p e r a t i n g

under boundary o r mixed l u b r i c a t i o n . S i n c e , a s h a s a l r e a d y been

mentioned, t h e h igh e l a s t i c i t y of t h e polymeric b e a r i n g bush i s

f avourab le t o t h e hydrodynamic l u b r i c a t i o n e f f e c t a t r e l a t i v e l y

low s l i d i n g speeds , t h e s l i d i n g speed a t which t h e f r i c t i o n coe f -

f i c i e n t i s l o w e s t , i . e . when t h e hydrodynamic e f f e c t b e g i n s t o oc-

c u r , shou ld be determined. The a u t h o r ' s s t u d i e s d e s c r i b e d elsewhere

( r e f . 360) have shown t h a t i n t h e c a s e o f m i n i a t u r e s t ee l -po lymer

j o u r n a l b e a r i n g s , t h e a n g u l a r speed o f t h e j o u r n a l a t which t h e

hydrodynamic l u b r i c a t i o n b e g i n s (w) can be expres sed by t h e f o r -

mula :

P Y hmin w = CK f i d

( 5 . 2 0 )

where C and K a r e p a r a m e t e r s , p i s t h e c o n t a c t p r e s s u r e , y t h e re-

l a t i v e c l e a r a n c e , hmin t h e minimum t h i c k n e s s o f t h e o i l f i l m ,

,u t h e v i s c o s i t y (dynamical) o f t h e o i l , and d t h e b e a r i n g h o l e d i -

ameter .

Taking i n t o accoun t t h e e l a s t i c i t y o f t h e s l i d i n g s u r f a c e , t h e

parameter C can be determined by f i r s t of a l l e s t i m a t i n g t h e c o e f -

f i c i e n t D i n t h e f o l l o w i n g way:

( 5 . 2 1 ) pd

Erhmin D =



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561

G r a p h i t i z a t i o n of ceramic

Greases , 54 s u r f a c e , 138

- f o r h i g h p r e s s u r e s and - - o p t i c a l i n s t r u m e n t s , 6 1 - - s e a l i n g , 57 - - s p a c e c r a f t mechanisms, 258 - t e s t i n g , 336, 401 - t h i x o t r o p i c , 6 1

Guides, 448 Gumz 's a p p a r a t u s , 374 Gyroscope b e a r i n g s , 438, 4 4 6

tempera tures , 6 1

Harmonic d r i v e s , 458 Hard c o a t i n g s , 285 - s e l f - l u b r i c a t i n g , 285

Hardness - of metals, 83 - of metal o x i d e s , 83

Heads, 1 4 6 , 437, 451, 487 Heart v a l v e p r o s t h e s i s , 499 H e a t - r e s i s t a n t polymers, 26, 32 High - molecular s u r f a c e a c t i v e

- p r e s s u r e o i l s , 4 4 - t empera ture o i l s , 4 4 - vacuum l u b r i c a t i o n , 4 6 , 57,

Hip j o i n t p r o s t h e s e s , 4 9 6 Holographic method, 395 Huber's method, 2 4 9 , 370 Human

a g e n t s , 277

258

- body, 8 - j o i n t s , 496 - t e e t h , 1 4 7 189, 418

Hydrodynamic l u b r i c a t i o n , 1 6 7 ,

Hydrogen wear, 506

I -coa t ings , 295 Impact wear, 4 9 4 Implants , 495 Incablock system, 431 Indium adhes ion t e s t , 389 I n d u s t r i a l g a s e s , 258 I n f r a r e d - spec t roscopy ( I R ) o f aged - thermometry, 331, 488

- non-metal l ic subs tance

- s o l i d l u b r i c a n t s , 70, 259 l u b r i c a n t f i l m s , 234, 381, 390

o i l s , 249

Inorganic

c o a t i n g s , 287

I n s p e c t i o n of epi lame o r

Ins t rument l u b r i c a n t s , 33

I n t e r a c t i o n s - i n oi l -polymer sys tems, 198, - i n solvent-polymer sys tems,

2 6 1 , 371, 376

383 I n t e r c a l a t i o n , 69 I n t e r n a l l u b r i c a t i o n , 19 , 32,

I n t e r n a l l y l u b r i c a t e d polymers,

Ion

181, 2 0 2

19, 32, 181

- - i m p l a n t a t i o n c o a t i n g s , 295 p l a t i n g c o a t i n g s , 273, 295

- s c a t t e r i n g spec t romet ry ( ISS) , - -

3 89

9 , 1 6 4 I ron-based s i n t e r e d materials,

Israe l a s h v i l y s formula , 9 5

J a s p e r , 1 6 J e w e l b e a r i n g s , 205, 2 9 9 , 405 J o u r n a l b e a r i n g s - polymer-polymer, 109, 1 9 7 , - p r i s m a t i c , 1 6 7 , 418 - s t e e l - b r a s s , 73, 152, 4 1 0 , - s t e e l - m i n e r a l , 131, 203, 405, - s tee l -polymer , 83, 173, 406

4 1 0

4 1 4

4 1 4

K i n e t i c s of recontaminat ion , 390 Kingsbury's d e s o r p t i o n model,

Knee j o i n t p r o s t h e s e s , 498 Knife-edge b e a r i n g s , 4 4 1

162

Laser t r e a t m e n t c o a t i n g s , 296 Laying d r o p method, 346 Lead films, 273 L e v i t a t i o n , 438 Liquid c r y s t a l s , 159 Low tempera ture o i l s , 4 4 , 255 L u b r i c a n t s , 33 - d u r a b i l i t y , 243 - g r e a s e s , 54 - oils, 33 - s o l i d , 68

L u b r i c a t i o n - of a r t i f i c i a l j o i n t s , 498 - boundary, 1 4 9 - of c o a t i n q s , 281 - of e l e c t r i c a l c o n t a c t s , 47,

61, 475 - under extreme c o n d i t i o n s , 253, - f o r - l i f e , 2 , 211, 443, 482 - of g e a r s , 458

443

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106

f o r c e d polymers has p robab ly a n adhes ive -de lamina t ion c h a r a c t e r

( r e f s . 2 1 1 , 215, 2 2 1 ) . F a t i g u e i s marked by growing c r a c k s which

s e p a r a t e t h e l a y e r from t h e b u l k mater ia l . The c r a c k s n u c l e a t e a t

t h e m a t r i x / r e i n f o r c i n g material p a r t i c l e i n t e r f a c e , p r o p a g a t e

p a r a l l e l t o t h e s u r f a c e ( t h e dep th depending on t h e f r i c t i o n coe f -

f i c i e n t ) and f i n a l l y s h e a r t o t h e s u r f a c e , producing w e a r s h e e t s .

S i n c e t h e c r a c k p ropaga t ion g e n e r a l l y c o n t r o l s t h e w e a r r a t e and

t h e c r i t i c a l d e p t h s a r e q u a s i - l i n e a r l y c o r r e l a t e d w i t h t h e f r i c -

t i o n c o e f f i c i e n t ( r e f . 2 2 1 ) t h e r e s h o u l d be a c o r r e l a t i o n between

t h e wear i n t e n s i t y of t h e r e i n f o r c e d polymer m a t e r i a l and t h e f r i c -

t i o n c o e f f i c i e n t . Such a c o r r e l a t i o n i s shown i n Fig. 4.18 (ref.196).

Friction coefficient

F i g . 4.18. R e l a t i o n s h i p between r a d i a l wear i n t e n s i t y o f polymeric bear ing bush i n m i n i a t u r e steel -polymer j o u r n a l bear ings and f r i c t i o n c o e f f i c i e n t . S l i d i n g speed v = 0.26 m/s, c o n t a c t pressure p = 0.075 MPa (dur ing wear t e s t s ) 1 - PC + 30% GF; 2 - PA 12 + 30% GF; 3 - PA 66 + 25% GF; 4 - POM c + 30% GF.





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5 4 3

69 4

695

696

6 9 7

6 9 8

699

70 0

70 1

70 2

70 3

704

70 5

7 0 6

7 0 7

70 8

709

7 1 0

7 1 1

7 12

713

7 1 4 715

7 1 6

7 1 7

7 1 8

K a t t e r l o h e r R. , Menzel K . : Linearmotor zum E i n s a t z b e i kryogenen Temperaturen. F e i n w e r k t e c h n i k + M e s s t e c h n i k 9 3 ( 1 9 8 5 ) 4, 165. B r i s t o w J.R. : K i n e t i c boundary f r i c t i o n . P r o c e e d i n g s o f t h e Roya l S o c i e t y o f London A189 (19471, 88. Rowson D . M . : A n a n a l y s i s o f s t i c k - s l i p motion. Wear 3 1 ( 1 9 7 5 ) 2, 213. K r a q e l s k i i I . V . , G i t i s N . V . : F r i c t i o n a l O s c i l l a t i o n s . Nauka, MOSCOW, 1957 , i n Russian. Soom A. , K i m C. : I n t e r a c t i o n s between dynamic normal and f r i c t i o n a l f o r c e s d u r i n g u n l u b r i c a t e d s l i d i n g . T r a n s a c t i o n s of t h e ASME - J o u r n a l o f L u b r i c a t i o n T e c h n o l o g y 1 0 5 ( 1 9 8 3 ) 2, 221. Michalec G . W . : P r e c i s i o n G e a r i n g T h e o r y and P r a c t i c e . J. Wiley, New York 1966 . Oleksiuk W . : F r i c t i o n i n F ine -P i t ch Gears. P o l i t e c h n i k a War- szawska , P r a c e Naukowe, Mechar i i ka 2 7 . Wydawnictwa P o l i t e c h - n i k i Warszawskiej , Warsaw 1975 , i n P o l i s h . Oleksiuk W . : Probleme d e r M i n i a t u r i s i e r u n g von F e i n g e r a t e - verzahnungen. F e i n g e r l t e t e c h n i k 2 7 ( 1 9 7 8 ) 4, 176. Roth K.: Anzeigen, Bedienelemente, Aufnehmer und G e t r i e b e i n zei tgemassen F e i n g e r a t e n . F e i n w e r k t e c h n i k + M e s s t e c h n i k 9 3 ( 1 9 8 5 ) 6, 301 . Yosimi S., e t a l . : Gears s i n t e r e d of i r o n powder. J a p a n e s e p a t e n t N o . 56-117779 ( 1 9 8 1 ) , i n J apanese . S c h o l t z G. : V e r s c h l e i s s v e r h a l t e n von spannend und durch S p r i t z g i e s s e n h e r g e s t e l l t e n K u n s t s t o f f z a h n r 3 d e r n r i n : K o n s t r u k t i o n , F e r t i g u n g und Anwendung f e i n w e r k t e c h n i s c h e r K u n s t s t o f f t e i l e , VDI-Verlag, Diiisseldorf 1976, p . 126. Erhard G. , S t r i c k l e E . : M a s c h i n e n e l e m e n t e aus t h e r m o - p l a s t i s c h e n K u n s t s t o f f e n . Band 2 . L a g e r u n d A n t r i e b s e l e m e n t e . 2. Aufl . VDI-Verlag , Diisseldorf 19 85. Krause W. ( e d . ) : P l a s t z a h n r s d e r . VEB-Verlag Technik, B e r l i n 19 85. Roth K. : Verschleissuntersuchungen an K u n s t s t o f f z a h n r a d e r n d e r Feinwerktechnik. V D I - B e r i c h t e ( 1 9 7 3 ) 195, 237 . N i l 1 E . : D i e Abriebsmessung an Verzahnungen d e r Feinwerk- t e c h n i k aus K u n s t s t o f f . U h r e n t e c h n i k ( 1 9 7 6 ) 2, 39. Klotzsche R. : Thermoplast ische Werkstof f e f i i r S t i r n r a d e r i n d e r F e i n g e r a t e t e c h n i k . F e i n g e r l t e t e c h n i k 2 7 ( 1 9 7 8 ) 5, 2 3 0 . Klo tzsche R. : Kinematische Genau igke i t s p r i t z g e g o s s e n e r P l a s t z a h n r s d e r . F e i n g e r z t e t e c h n i k 32 ( 1 9 8 3 ) 7, 303. Roth K., K o l l e n r o t t F.: Zahnradpaarungen m i t Komplement- p r o f i l e n z u r E rwe i t e rung d e r E i n g r i f f s v e r h a l t n i s s e und ErhSrung der Fuss- und F l a n k e n t r a g f a i g h e i t . K o n s t r u k t i o n 34 ( 1 9 8 2 ) 3, 81. Szczec ina H . : Technische Prazisions-Kunststoffteile. F e i n w e r k t e c h n i k + M e s s t e c h n i k 9 0 ( 1 9 8 2 ) 3, 129. G i r a u d i C. : E r r e i c h b a r e Toleranzen und Q u a l i t z t von Kunst- s t o f f z a h n r s d e r n i n d e r Feinwerktechnik. F e i n w e r k t e c h n i k + M e s s t e c h n i k 9 0 ( 1 9 8 2 ) 7, ZM 6. D r i v e l i n e components. M a c h i n e D e s i g n 5 7 ( 1 9 8 5 ) 15, 7. Walker T. : Rat ing f i n e - p i t c h boundary - lub r i ca t ed g e a r s . Power T r a n s m i s s i o n D e s i g n 1 5 ( 1 9 7 3 ) Octobe r , 62. Vorbach G. , Bednarz J. : Thermoplast m i t Flammschutzausrustung f u r r e inbungsbeansp ruch te T e i l e d e r E l e k t r o - und Feinwerk- t e c h n i k . F e i n w e r k t e c h n i k + M e s s t e c h n i k 72 ( 1 9 8 2 ) 5, 286. Ivanov M . I . : H a r m o n i c D r i v e s . Vysheysha Shkola , Minsk 1981 , i n Russ i an . Ca r l son J . H . : Harmonic d r i v e s f o r servomechanisms. M a c h i n e D e s i g n 5 7 ( 1 9 8 5 ) 1, 102.

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wear depends on t h e b r i t t l e n e s s a s w e l l as t h e hardness o f t h e m a t e r i a l used . The microhardness of t h e aforementioned materials

is 23600, 2 2 2 0 0 , 14700, 12780, 8840 and 4400 MPa, w h i l e t h e micro-

b r i t t l e n e s s ( d e f i n e d as microhardness a t 0 . 0 0 1 N when 50% of in-

d e n t a t i o n s t u r n i n t o c r a c k s ) i s 1 4 0 , 4 2 , 26, 182, n o t e s t i m a t e d

and 4 8 MPa r e s p e c t i v e l y . The wear of hardened f r e e - c u t t i n g steel

rubbing a g a i n s t s a p p h i r e , ruby , fused q u a r t z , a g a t e , d i a s p o r e and

g l a s s i s t a k i n g t h e wear when rubbing a g a i n s t s a p p h i r e as 1 . 0 , as

fo l lows: 1 .3 , 1.1, 1.1, 1 . 6 , 1 .3 . It can be seen t h a t when a series

of m i n e r a l s of i n c r e a s i n g hardness a r e t e s t e d , t h e wear of t h e

s teel element f i r s t i n c r e a s e s and then d e c r e a s e s . The i n c r e a s e i n

wear i s connected w i t h t h e hardness of t h e a b r a s i v e p a r t i c l e s

(wear d e b r i s of t h e m i n e r a l s ) i n t h e f r i c t i o n area. The wear in-

c r e a s e s w i t h i n c r e a s e of l o a d .

T h e o r e t i c a l and exper imenta l s t u d i e s u s i n g a f o u r - b a l l f r i c -

t i o n machine i n which t h e upper b a l l w a s made of s a p p h i r e and t h e

lower b a l l s of hardened f r e e - c u t t i n g s tee l o r WC 1 0 t u n g s t e n

c a r b i d e ( r e f . 9 5 ) , have shown t h a t t h e r e l a t i o n s h i p between t h e

wear i n t e n s i t y , I,, of steel o r WC 1 0 materials as a f u n c t i o n of

t h e maximum r e a l c o n t a c t p r e s s u r e pm can be approximated w i t h t h e

fo l lowing formula:

(4 .38)

-9 where a l l and a12 can be taken a s 3.13 1 0 and 0 . 4 f o r f r e e -

- c u t t i n g s tee l and 5 . 0 10 - l ' and f o r WC 1 0 r e s p e c t i v e l y . 6.0

The wear of t h e ceramic m a t e r i a l s depends on t h e rubbing con-

d i t i o n s . For i n s t a n c e , a t low s l i d i n g s p e e d s , a g a t e wears l i k e a

p l a s t i c material b u t a t high s l i d i n g speeds t h e wear i s s i m i l a r t o

t h e wear of very b r i t t l e materials ( r e f . 9 5 ) . The wear i s propor-

t i o n a l t o t h e s l i d i n g d i s t a n c e . The roughness of t h e s u r f a c e s of

t h e rubbing e lements has an impor tan t e f f e c t on t h e t r i b o l o g i c a l

p r o p e r t i e s of t h e m a t e r i a l combinat ions be ing c o n s i d e r e d .

For m i n i a t u r e t r i b o l o g i c a l systems t h e optimum s u r f a c e rough-

n e s s of t h e rubbing e lements depends on whether t h e y are i n t e n d e d

f o r a s h o r t o r long s e r v i c e l i f e ( r e f . 256) . I n t h e f i r s t case t h e

optimum s u r f a c e roughness w i l l be when t h e f r i c t i o n is a t i t s min-

i m u m and i n t h e second when t h e f r i c t i o n i s s t a b l e and t h e wear is

minimum. The minimum f r i c t i o n i s a f u n c t i o n of t h e i n i t i a l rough-

ness and s t a b l e f r i c t i o n i s a f u n c t i o n of t h e roughness a f t e r t h e

running-in p r o c e s s . I n microbear ings which have ruby jewels w i t h a

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131

4 ,3 , OTHER SYSTEMS

Many of the tribologicaL systems used in small mechanisms have

elements made of non-metallic and non-polymeric materials or have

polymeric elements rubbing against elements made of various other

materials. Typical of these are ceramic materials such as sapphire

or ruby (single-crystal aluminium oxide) , used for many years in the bearings of precision instruments (jewels). A steel, roller-

-burnished journal usually ruhs against such bearings. The fric-

tion and wear of elements in such a material combination is highly

dependent on rubbing conditions.

The friction coefficient of typical free-cutting steel (harden-

ed) rubbina against sapphire is about 0 .5 and of bearing stainless

steel about 0.4 (ref. 9 5 ) . The effect of the hardness of materials

rubbing against sapphire was found to be that when the metal or

ceramic material is harder the friction coefficient is lower. The

friction coefficient of monel alloy is 0.52, while for WC 2 0 (WC + 2 0 % Co), WC 1 0 tungsten carbides and sapphire, with microhardness

11000 , 16000 and 22500 MPa respectively, it is 0.35, 0 . 3 2 and 0 .30

respectively. The friction (and wear) characteristics are aniso-

tropic. The tribological properties of spherical microbearings,

which have a steel element rubbing against corundum depend on the

orientation on the optical axis of the crystal to the friction

surface: the friction torque (as a function of the sliding dis-

tribology of miniature systems tribology series 13

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