TECHNICAL SITALLS* SUITABLE FOR OPERATION

UNDER UNLUBRICATED FRICTION CONDITIONS

N. D. Nazarenko, I~. T. Mamykina, A. I. Yunga, and N. I. Vlasko

UDC 621.762

Nothing appears to have been published to date in the l i te ra ture on the antifrict ion charac te r i s t i c s and wear res is tance of microcrys ta l l ine glasses . It is interest ing to note, however, that P y r o c e r a m glass has been used in the United States under unlubricated fr ict ion Conditions at t empera tures up to 540~ and also that Sital113-56 has been employed in the Soviet Union in applications involving fr ict ion in cor ros ive environ- ments [1].

In the p resen t work, determinat ions were made of the antifrict ion p roper t i e s and wear res is tance of a microcrys ta l l ine glass developed by the authors. The mater ia l , provisional ly called Sitall 3, is produced by the glassmaking technique. It is vir tually nonporous, and has a compress ive strength of 8000-12,000 kg / cm 2 and an impact s trength of 5.5-6 k g - c m / c m 2. Fr ic t ion tests were per formed, using the shaf t -and- inser t scheme, in MT-62M, MTV-22M, and M-27 testing machines [2, 3]. With these machines, it is poss i - ble to va ry sliding veloci t ies and loads on contact surfaces within wide l imits, and also to record in the course of experiments the l inear wear of the fr ict ion pair , the fr ict ional force, and the tempera ture in the fr ict ion zone. In the tests , in which no fr ict ion zone lubrication was employed, Sitall 3 specimens rubbed against quenched Type 45 steel, T15K6 hard alloy, and 1Kh18N9T stainless steel in air, and also against quenched Type 45 steel in a vacuum of 5 �9 10 -5 torr .~

To shorten the running-in t ime of fr ict ional pairs , the Sitall 3 specimens were ground, af ter being mounted in the fr ict ion machine, with a diamond disk of the same diameter as the mating par t used in the subsequent test.

Initially, tes ts were conducted at a constant p r e s su re of 10 k g / c m 2 and sliding veloci t ies ranging f rom 2 to 12 m/sec . Next, the load on all mater ia l s which had proved capable of operating in a stable manner in this sliding veloci ty range was ra ised in steps, at a veloci ty of 12 m/sec , to levels causing ei ther a sharp r i se in the fr ict ional force or catas t rophic wear of the rubbing surfaces . Finally, the mate r ia l s exhibiting the best antifriction proper t i es were tested in a vacuum.

TABLE i. F i r s t Series of Experiments , with Quenched Type 45 Steel as Mating Material

Material

Control Sitall Sitall 3 Sitall 3 with

(NH4)2MoO 4 ad- dition

Sliding velocity 2 rn/sec 12 m/sec

coeff, of wear friction, rate ~,. II g/kin

0,12 2 0,12 4 0,14 3

coeff, of friction, It

0,17 0 , 1 1

0,14

wear rate ,5, kl ]krn

7 6

10

The f i rs t se r ies of experiments , the resul ts of which are presented in Table 1, demonstrated that, at a p r e s s u r e of 10 kg / cm 2, the antifriction proper t i es and wear res i s tance of the standard Sitall m i c r o c r y s - talline glass used as a control and the experimental Sitalls investigated was hardly affected by sliding veloci ty variat ions. Nevertheless , the coefficient of

*Microcrys ta l l ine g lasses - Transla tor . $ The following mater ia l s are r e fe r r ed to in this ar t icle: Type 45) a 0.45% C steel; 1KhlSN9T) a Ti- stabilized 18/8 stainless steel; T15K6) a WC + 15% TIC+6% Co hard alloy; VKS) a WC+8% Co hard alloy - Transla tor .

Institute of Mater ia ls Science, Academy of Sciences of the Ukrainian SSR. Translated f rom Porosh- kovaya Metallurgiya, No. 5 (113), pp. 75-77, May, 1972. Original ar t ic le submitted May 5, 1971.

�9 Consultants Bureau,. a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher, d copy of this article is available from the publisher for $15.00.

399

Y ..... " [a,./~/kn.-/ [ J , o,3o . . . .

o,e ------- i

o, eo i a

" - ' - - - 6 ov, O,/O ~ 8 I0 v,. mhec

Fig. 1. Var ia t ion of coeff ic ients of f r ic t ion and l inear w e a r r a t e s of Sitalls with sliding ve loc i ty and mat ing p a r t ma te r i a l . Mating p a r t ma te r i a l : 1) quenched Type 45 s teel ; 2) 1KhlSN9T; 3) VKS. T e s t s in a i r at P = 10 k g / c m 2 .

Fig. 2. Fr ic t ion su r face of Sitall 3 a f t e r t es t s in: a) a i r ; b) vacuum of 5 . 1 0 -5 t o r r . • 250.

. / 0,6

2 ' J " @ ~ 5 ~.......~,,"

0,30

t

fo 20 30 P, kg/cmz

Fig. 3. Effect of envi ronment on coeff ic ient of f r ic t ion of Sitall 3: 1) a i r ; 2) vacuum of 2" 10 -~ to r r . V =1 m / s e c , r u b - bing against quenched Type 45 steel .

f r ic t ion of the control Sitall did show a tendency to i n c r e a s e with r i s e in sliding velocity, Thus, va lues of coefficient of f r ic t ion of 0.12 and 0.17-0.19 at sliding ve loc i t i e s of 2 and 12 m / s e c , r e spec t ive ly , were r e c o r d e d fo r this ma te r i a l . F o r our Sitall 3, the coeff ic ients of f r ic t ion at 2 and 12 m / s e c w e r e 0.12 and 0.11, r espec t ive ly .

In t e s t s involving rubbing agains t 1Khl8N9T s ta in less s tee l and VK8 hard alloy, the p r o p e r t i e s of the Sitalls w e r e found to va ry , as a function of sliding veloci ty, in the s ame way as when quenched Type 45 s tee l was used as the mat ing m a t e r i a l (Fig. 1). The highest va lues of coeff icient of f r ic t ion w e r e r eco rded for the Sitalls rubbing against the s t a in les s steel . The highest va lues at tained under these conditions w e r e 0.43-0.41 fo r the control Sitall and 0.25 for Sitall 3. The coeff i - c ients of f r ic t ion of the Sitalls rubbing againstVK8 hard alloy were a lso much higher than those m e a s u r e d in expe r imen t s in which Type 45 s teel was the mat ing ma te r i a l .

When a Sital l g l a s s rubs agains t s teel , a s table f i lm f o r m s on the working sur face of the spec imen (Fig. 2a); f r ic t ion in a vacuum does not lead to the fo rmat ion of such a f i lm, but, instead, t r a n s f e r of the mat ing pa r t m a t e r i a l onto the Sitall su r face and smea r ing of the m a t e r i a l a r e obse rved (Fig. 2b). In the vacuum tes t s , the opera t ing behav ior of all the m a t e r i a l s inves t igated proved to be unsa t i s fac tory . The coeff ic ients of f r ic t ion of the p a i r s tes ted sharp ly i nc rea sed under these conditions, at taining va lues of 0.64-0.8 (Fig. 3). Thus, i t may be a s sumed that the low coefficient of f r ic t ion of a Sitall rubbing against Type 45 s tee l i s due to the fo rma t ion of p ro tec t ive f i lms as a r e su l t of the p r o c e s s e s of oxidation of the s tee l and subsequent t r a n s f e r of oxidation p roduc t s onto the Sitall.

It should be noted that the fo rmat ion of such f i lms and the marked fall in the coefficient of f r ic t ion take p lace when the su r face of a Sitall r eaches a t e m p e r a t u r e of at l eas t 400 ~ C. The lowering of the

400

coefficient of friction is accompanied by some decrease in wear resistance. Under severe operating con-

ditions (particularly at high pressures), the concentration of heat in the active working layer of a Sitall specimen causes, owing to the low thermal conductivity of the material, the temperature in a 500-700-# surface layer of a Sitall 3 specimen to rise to 650-700~ As a result, the linear wear of the frictional

pair sharply increases. Because of this, in the manufacture of a moving joint with a friction pair one ele- ment of which is made of a Sitall glass, it is necessary to ensure that the contacting surfaces fit well if the pair is to give long and trouble-free service. In the case of an appreciable overlap, intensified cooling of the friction zone may be required.

The results of this friction and wear investigation demonstrate that Sitall 3 can be regarded as a po- tentially useful base material for the development of a microcrystalline glass with attractive antifriction characteristics.

i I 2.

3.

L I T E R A T U R E C I T E D

B. D. Voronkov, Dry Friction Bearings [in Russian], Mashinostroenie, Leningrad (1968). t~. T. Mamykina et al., in: Increasing the Wear Resistance and Useful Life of Machines [in Russian], Izd-vo AN UkrSSR, Kiev (1966). L. F. Kolesnichenko et al., Poroshkovaya Met., No. 3 (1970).

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