WEAR

RESISTANCE

MATERIALS

SLIDING

SOLUTIONS Yu. and

OF

OF M. V.

METAL-GLASS IN

CAUSTIC

Kolobov, E. G. Mel'nikov

AQUEOUS SODA V.

Lyalin,

UDC 62L762 + 620.194.3 + 661.322

It has b e e n e s t a b l i s h e d by many i n v e s t i g a t o r s that p o r o u s s i n t e r e d b e a r i n g s a r e w e l l - s u i t e d f o r u s e in sliding units operating in t y p e s of s e r v i c e w h e r e good w e a r r e s i s t a n c e , low coefficients of friction, and high r e l i a b i l i t y a r e i m p o r t a n t r e q u i s i t e s . Now powder m e t a l l u r g y techniques m a k e it possible to produce p a r t s f r o m v a r i o u s m i x t u r e s whose c o m p o n e n t s differ widely in t h e i r p h y s i c o m e c h a n i c a l p r o p e r t i e s [1]. A typical e x a m p l e of such m a t e r i a l s , which w a s chosen f o r the p r e s e n t investigation, is provided by sintered i r o n containing g l a s s inclusions. The p o s s i b i l i t i e s opened up by the u s e of such m a t e r i a l s in f r i c t i o n units a r e d i s c u s s e d in [2]. In the p r e s e n t work, a study was made of the w e a r r e s i s t a n c e of m a t e r i a l s produced by s i n t e r i n g PZh2M fine reduced iron powder (to GOST 9849-61 standard) with additions of 3% of ~ I G - I I graphite (to GOST 10274-62 standard), 2% of molybdenum disulfide, and 1, 3, 5, 7, o r 10 wt.% of VVS g l a s s of standard c o m p o s i t i o n [3]. The c h e m i c a l c o m p o s i t i o n s , p a r t i c l e size a n a l y s e s , and p h y s i c o m e c h a n i c a l c h a r a c t e r i s tics of the s t a r t i n g powders w e r e identical with those given in [4, 5]. To i m p r o v e the c o m p r e s s i b i l i t y of the powders and reduce the w e a r of the tool (die and punch) m a t e r i a l s , 1% of zinc s t e a r a t e was added to the powder c h a r g e s . G l a s s p o s s e s s e s c e r t a i n p r o p e r t i e s enabling it to be used s u c c e s s f u l l y as h a r d inclusions [2, 6],while, as h a s b e e n noted by Matsin, Shpagin, and K r a g e l ' s k i i [7-9], the p r e s e n c e of h a r d g r a i n s in a c o m p o s i t e b e a r i n g m a t e r i a l s t r e n g t h e n s its ductile m a t r i x , e n s u r e s a u n i f o r m distribution of p r e s s u r e o v e r the shaft j o u r n a l , and p r e v e n t s s e i z u r e f r o m Occurring o v e r l a r g e p a r t s of the b e a r i n g . At the sintering t e m p e r a t u r e s of i r o n - g r a p h i t e c o m p o s i t e s , g l a s s is in a softened condition and h a s a v i s c o s i t y which is low enough to enable it to flow f r e e l y into p o r e s [10]. After sintering, g l a s s g r a i n s in an i r o n - g r a p h i t e c o m p o s i t e a r e f r e e f r o m s h a r p edges, and t h e r e is thus no r i s k of a b r a s i v e w e a r or m i c r o c u t t i n g of friction s u r f a c e s . With suitably chosen m e t a l l i c constituents and mating p a r t m a t e r i a l s , m e t a l - g l a s s c o m p o s i t e s can exhibit high w e a r r e s i s t a n c e , f o r in such a c a s e it is possible to satisfy the b a s i c r u l e of f o r m u l a t i o n of a w e a r r e s i s t a n t m a t e r i a l , n a m e l y , that a soft m e t a l l i c m a t r i x should be combined with hard (glass) inclusions. A p a r t f r o m this, a m e t a l - g l a s s m a t e r i a l p o s s e s s e s good c o r r o s i o n r e s i s t a n c e , since its o p e n p o r e s a r e filled with g l a s s , which p r e v e n t s a g g r e s s i v e r e a g e n t s f r o m p e n e t r a t i n g into the m a t e r i a l [11]. Consequently, m e t a l - g l a s s m a t e r i a l s would be expected to be p a r t i c u l a r l y effective in friction units of m e c h a n i s m s and m a c h i n e s whose journal b e a r i n g s o p e r a t e in d i r e c t contact with c o r r o s i v e liquid media. In our w o r k , c h a r g e s w e r e p r e p a r e d by a c c u r a t e l y weighing out, to :~10 m g , and thoroughly mixing the c o m p o n e n t s without lubricant. Specimens w e r e c o m p a c t e d in a hydraulic p r e s s under a p r e s s u r e of 5.5 t o n s / c m 2 and then s i n t e r e d f o r 1.5 h at 1050-1060~ in a Ts]~P-356 f u r n a c e provided with a hydrogen a t m o s p h e r e . The r e s u l t a n t s p e c i m e n s had a p e a r l i t i c - f e r r i t i c s t r u c t u r e and a m a e r o h a r d n e s s of 52-68 HB. T h e i r p o r o s i t y a f t e r s i n t e r i n g w a s 25-30%. They w e r e not i m p r e g n a t e d with oil b e f o r e being tested. The w e a r r e s i s t a n c e of the m e t a l - g l a s s m a t e r i a l s w a s investigated, using a modified MI-1M f r i c t i o n m a c h i n e , in distilled w a t e r and 5-35% solutions of caustic soda at sliding s p e e d s of 0.4-1.3 m / s e e . In the Ivanovo C h e m i c a l Technology Institute. T r a n s l a t e d f r o m P o r o s h k o v a y a Metallurgiya, No. 12 (132), pp. 81-84, D e c e m b e r , 1973. Original a r t i c l e submitted June 21, 1972. 9 1974 Consultants Bureau, a division o f Plenum Publishing Corporation, 227 ~'est 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in, any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy o f this article is available from the publisher for $15.00.

1008

~?,1

la

r

I

v lll\\l

l

t El / bttl]j

,~'# I\kk] m'k ,t | i

; JIIJ 3

5 7

10

!

3

5

7

/0

o!

3

5

7

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o!

IN 1 5 7 to

~

Glass content, wt.% Fig. 1. Intensity of w e a r of sintered m a t e r i a l s as function of glass content, type of medium, and sliding speed: 1) 0.42; 2) 0.84; 3) 1.28 m / s e c . Medium: a) distilled water; b-d) 5, 15, and 35% solutions of NaOH, r e s p e c t i v e l y . testing scheme employed, an insert segment slid on a mating part. The mating part was a 40-ram diameter x 10-mm wide roller made of 40Kh low-alloy chromium steel (48-52 HRC). The testing conditions chosen were similar to those under which journal bearings normally operate in the mercerization vats of textile dyeing and finishing plants. Specimen wear was determined by the "false base" method. Pressure was applied to the specimen by means of a lever. The temperature in the friction zone was measured with a Chromel-Alumel thermocouple whose hot junction was located at a distance of 0.5-1 mm from the friction surface of the specimen. For purposes of comparison, similar tests were carried out on commercially produced ZhGr-3 sintered antifriction material (97% Fe + 3% C). The results of wear tests conducted on these sintered materials in various media under a pressure of 15 kg/cm2 are shown in Fig. i. It follows from these data that the addition of VVS glass to the charge increases the wear resistance of sintered materials sliding in aqueous solutions of caustic soda. Commercially produced ZhGr-3 material is less wear resistant. The lowest intensity of wear is exhibited by a sintered material containing 7% of glass, whose wear resistance is about 2.5-5 times that of ZhGr-3. With increase in NaOH concentration, the intensity of wear of the materials investigated falls. Thus,raising the concentration of NaOH from 5 to 35% reduces the intensity of wear of all the materials investigated by some 35-50%. This is borne out by decreased values of coefficient of friction. The improved wear resistance may be attributed to the growth in the strength of the metallic skeleton brought about by the increase in the amount of the hard glass phase, which is uniformly distributed throughout the soft iron matrix. Apart from this, as has been demonstrated in [3], the mierostructure of sintered metal-glass materials contains several other phases in addition to the metallic matrix and glass. These phases are in the form of crystals (hedenbergite, fayalite, ferrosilite, ~kermanite), which may, depending on their physicomechanical characteristics, act as hard inclusions or as solid lubricant in the course of sliding. The improvement in wear resistance can be linked also with the chemical action of aqueous solutions of caustic soda on sliding metal-glass composite surfaces. According to [12, 13], silicates on a glass surface react with water to form a caustic alkali and a silicic acid gel. The resultant impervious gel film protects the surface against corrosion and mechanical attack and provides additional lubrication. The intensity of wear of a metal-glass specimen apparently depends on the degree of removal of the gel film from its sliding surface. It should also be noted that raising the concentration of an alkali solution markedly increases its viscosity, which improves the lubricating power of the medium and may produce a transition to a dual mechanism of friction, leading to a decrease in the intensity of wear of specimens. C~ar experiments have shown that the least intensity of wear and the lowest value of coefficient of friction in all the media investigated are exhibited by a sintered material with a glass content of 7%.

1009

90 80

= 4o4 2 o, o3

70

1

/

50

j7

4o;

o,,oi>'--,. o 900

1800

900

2700 n./0,Jrevs.

Fig. 2. Variation of coefficient of f r i c t i o n with testing t i m e : 1) Z h G r 3; 2) sintered m a t e r i a l with 7% of glass.

/800

I

2700 n.iO"J, revs.

Fig. 3. Variation of extent of w e a r with testing t i m e . Designations as for Fig. 2.

In the next phase of investigation, stand t e s t s w e r e c a r r i e d out on this p a r t i c u l a r m a t e r i a l , using a DM-29 f r i c t i o n machine, in a 35% solution of caustic soda at a sliding speed of 1.25 m / s e e and a p r e s s u r e of 25 k g / c m 2. The r e s u l t s of t h e s e t e s t s a r e p r e s e n t e d in Figs. 2 and 3. It will be seen that, under steadys t a t e conditions of operation, the coefficient of f r i c t i o n of the new m a t e r i a l w a s found to be much l e s s than that of Z h G r - 3 . The w e a r of bushings m a d e in the new m a t e r i a l w a s only about a q u a r t e r to one-third that of Z h G r - 3 bushings. In the c a s e of Z h G r - 3 bushings, the bushing m a t e r i a l seized with the shaft m a t e r i a l a f t e r 56 h o u r s ' operation, as a r e s u l t of which the coefficient of friction and bushing w e a r s h a r p l y i n c r e a s e d and the bushings c e a s e d to function effectively a s b e a r i n g s . The operating b e h a v i o r of the s i n t e r e d m a t e r i a l containing 7% of VVS g l a s s w a s e n t i r e l y s a t i s f a c t o r y . After 100 h o u r s ' operation, the shaft and bushing s u r f a c e s had a C l a s s 9 or 10 finish (initially, the s u r f a c e finish of both c o m p o n e n t s w a s of C l a s s 7). CONCLUSIONS I. It is shown that metal-glass composites can be successfully used as ant[friction materials for journal bearings operating in aqueous solutions of caustic soda. 2. A study was made of the wear resistance of sintered iron base ant[friction materials with additions of 1-10% of VVS glass, graphite, and molybdenum disulfide. 3. The optimum glass content, giving the least wear under the testing conditions selected, was determined. LITERATURE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13"

1010

and the lowest value of coefficient of friction

CITED

A . F . Beloivan, G. V. Isakhanov, et al., P o r o s h k o v a y a Met., No. 5 (1966). S . G . K a v e r i n , Vopr. Mekhan., No. 2 (1965). R . V . Vlasyuk, E. S. L u g o v s k a y a , and I. D. R a d o m y s e l ' s k i i , P o r o s h k o v a y a Met., No. 3 (1969). I . D . R a d o m y s e l ' s k i i and N. I. Shcherban', P o r o s h k o v a y a Met., No. 4 (1966). V . E . Vainshtein and G. I. T r o y a n o v s k a y a , D r y L u b r i c a n t s and S e l f - l u b r i c a t i n g M a t e r i a l s [in R u s sian], M a s h i n o s t r o e n i e , Moscow (1968). A Handbook of M a t e r i a l s in E n g i n e e r i n g [in Russian], Vol. 5, M a s h i n o s t r o e n i e (1969). E . A . Matsin, The Charpy Rule and the Surface M i c r o r e l i e f of Ant[friction Alloys, T r a n s s c t i o n s of the Second All-Union C o n f e r e n c e [in Russian], Vol. 3, Izd-vo AN SSSR, Moscow (1949). A . I . Shpagin, Ant[friction Alloys [in Russian], Metallurgizdat (1956). I . V . K r a g e l ' s k i i , F r i c t i o n and W e a r [in Russian], Mashgiz (1968). R . Z . Vlasyuk and I. D. R a d o m y s e l ' s k i i , P o r o s h k o v a y a Met., No. 11 (1969). V . A . Suprunov and V. N. K i s e l ' n i k o v , Izv. Vysshikh Uchebn. Z a v e d e n i i , Khim. i Khim. Tekhnol., 6, No. 4 (1963). A . A . Appen, The C h e m i s t r y of G l a s s [in Russian], Khimiya (1970). I . t . K i t a i g o r o d s k i i (editor), G l a s s Technology [in Russian], Moscow (1967).