HYDROABRASIVE

WEAR

A. I. Slyn'ko, G. and N. A. Sologub

OF A.

IN

METALS

ALKALINE

MEDIA UDC 620.193,1

Preis,

Most investigators of hydroabrasive wear of metals have used tap water as the carrier of the abrasive particles and have concluded that the process is the result of the mechanical influence of the abrasive and the stream of fluid. However, hydroabrasive wear in water is also affected by corrosion. Furthermore, operating conditions where abrasive particles are suspended in other liquids are encountered in practice. We made tests to determine the effect of several factors (testing time, concentration of abrasive, and relative speed) on hydroabrasive wear of several metals in tap water and lime water (pH = 12.6). Steels 45 and IKh18NIOT, cast iron SCh 18-36, and bronze BrAZh 9-4 were also tested in a solution of caustic soda. The experiments were made in a modified jet-impact apparatus [I]. The concentration of abrasive was 3%, the length of the tests was 105 impacts of the jet, the speed of impact was 29 m/see, and the temperature of the fluid was 50~ Quartz sand with grain sizes of 100-200 # was used as the abrasive~ The resistance of the metals was determined from the weight loss. Normalized steel 45 was used as a standard for determining the relative resistance. The samples were examined visually and in a microscope, and the surface hardness was measured. The tests showed (Fig~ i) that for steels 45 and IKhI8NIOT, cast iron SCh 18-36, and bronze BrAZh 9-4 the relationship between the weight loss and the length of the test and concentration of abrasive is linear in both tap water and lime water and can be described by the equations

AG = ,/G t,

(I)

dt

80

~~~.

~0

80

/

f#

2//

dO f

/

~"

/

..JJd-'%

__.1__

0

2

4

N,~fO 5

Fig. i. Relationship between BrAZh 9-4 (I), cast iron SCh (3) and 45 (4) with the number concentration of abrasive (C) lime water (solid lines).

O

2

I

t

4,

6'

t

,.--]

~ c,~

loss of mass (Am) of bronze 18-36 (2), and steels IKhI8NIOT of impacts of the stream (N) and in tap water (dashed lines) and

Kiev Technological Institute of the Food Industry. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 8, No. 2, pp. 9-13, March-April, 1972. Original article submitted February i0, 1971. 9 Consultants Bureau, a division o f Plenum Publishing Corporation, 227 West 17th Street, New York, .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, photoeopying, microfilming, recording or otherwise, without written permission of the publisher. ,[ copy of this article is available from the publisher for $15.00.

133

TABLE 1. Loss of Mass (mg) by Hydroabrasive Wear in Different Media MeAium

~ 13,3

Lime Water

g'o~,

?

-,,'=,~ "I '.,~b "~ ~ I o,~? ~N

22,3 14,8 33,3

Caustic sodasolution 18,6

30,3

17,0 30,6

Tap water

50,6

18,8 28,4

25,7

TABLE 2. Loss of Mass (rag) During Hydroabrasive Wear T e s t s in Lime Water at Different T e m p e r a t u r e s

15 40 70

4,4 5,9 7,9

dG dt

--

25 ~O I 40

On,

6,0 [ 6,7 9,2

10,5 13,2 17,5

(2)

where &G is the loss of m a s s at time t; dG/dt is the rate of m a s s loss at a given concentration of a b r a s i v e ; n is the concentration of a b r a s i v e ; b is the proportionality factor. Substituting Eq. (2) into (1), we find AG = bnt. According to l i t e r a t u r e data [2], the value of b depends on the p r o p e r t i e s of the metal and the testing conditions (velocity of the s t r e a m , angle of attack, etc.). As our experiments showed, this factor also depends on the chemical composition of the medium - it is s m a l l e r for steel 45 and cast iron SCh 18-36 in lime water (and l a r g e r for bronze BrAZh 9-4) than in water.

t

J J8

=

8,5 9,9 13,8

I 50

t V, m/sec

Fig. 2. Effect of impact velocity (V) on the ratio of m a s s l o s s e s in tap water (mtap) and lime water (mlime). 1) Steel G13; 2) c a s t iron SCh 18-36; 3) steel 45; 4) steel 1KhlSN10T.

The velocity of the impact of the s t r e a m on the samples has different effects on the wear rate of steels 45 and G13, and also c a s t iron SCh 18-36, in both media (Fig. 2). For steel 45 and c a s t iron SCh 18-36 at velocities of 29 m / s e c , and for steel G13 at all v e l o c i ties tested, the damage in lime water is s m a l l e r than in tap water. The wear of steel 1KhlSN10T was a l m o s t identical at all velocities tested. It was found f r o m the m i c r o s c o p i c examination that the c h a r a c t e r of failure does not change with the impact velocity. The principal factor in the w e a r of these metals at all velocities is the mechanical factor, and t h e r e f o r e the r e s i s t a n c e depends mainly on the strength c h a r a c t e r i s t i c s .

The relative r e s i s t a n c e of the metals investigated and the o r d e r of their r e s i s t a n c e to h y d r o a b r a s i v e wear differed in tap water and lime water (Fig. 3). This is due to the fact that for many metals, including the standard, the loss of m a s s in lime water differs f r o m that in tap water. F o r F e - C alloys in lime water it depends on the amount of pearlite, while for c a s t iron it also depends on the shape of graphite inclusions. The r e s i s t a n c e in this medium is high for heat t r e a t e d steels and steels with a high c a r b o n content (pearlite), chromium cast iron Kh15M, and steel G13. The r e s i s t a n c e s of steel 1KhlSN10T, VT1 titanium, and B r A Z h 9-4 bronze are relatively low. In caustic sodathe h y d r o a b r a s i v e wear of steel 45 and e a s t iron SCh 18-36 is also less intensive than in tap water. The loss of m a s s is almost independent of the medium for steel 1Kh18N10T and bronze BrAZh 9-4 bronze are r e l a t i v e l y low. The difference in the s e q u e n c e of the r e s i s t a n c e of the metals and the values of the loss of m a s s in alkaline media as c o m p a r e d with tap water is due to the c o r r o s i o n factor. Under the influence of the h y d r o a b r a s i v e s t r e a m the c o r r o s i o n p r o c e s s e s on the surface of c a r b o n steels and c a s t irons, intensified by plastic deformation, a r e a c c e l e r a t e d , and t h e r e f o r e the loss of m a s s is l a r g e r than in the alkaline media, other conditions being equal. The large difference in the loss of m a s s of c a s t iron samples in tap water and 'alkaline media is also due to e l e c t r o c o r r o s i o n p r o c e s s e s in the water due to the heterogeneity of the s t r u c t u r e [4]. In alkaline media F e - C alloys f o r m thin passive films of c o r r o s i o n products and absorbed OH ions [5]. It was found in [6-8] that the incubation period of h y d r o e r o s i o n wear of c a r b o n steels and cast i r o n s in alkaline media is shortened in the p r e s e n c e of these films. Due to their strength and adhesion to the base metal, the films also reduce the destructive effect of the a b r a s i v e p a r t i c l e s . At high flow r a t e s ,

134

J,O

,

~

Ps#

- ~

J

$0 Fig. 3

I

t,

60 gO 128 Time, Sec Fig. 4

Fig. 3. Relative r e s i s t a n c e to h y d r o a b r a s i v e w e a r in l i m e w a t e r (white columns) and tap w a t e r (shaded columns). 1) A r m c o iron; 2) steel 45; 3) steel US; 4) c a s t iron SCh 12-28; 5) c a s t iron SCh 18-36; 6) chilled iron; 7) c a s t i r o n VCh 50-1.5; 8) c a s t iron Khl5M (annealed); 9) c a s t iron Khl5M (HRC = 50-55); 10) steel 1Khl8N10T; 11) VT1 titanium; 1 2 ) b r o n z e B r A Z h 9 - 4 ; 13) steel 45 (HRC 52-55); 14) steel 45 (HRC = 45-48); 15) steel G13. Fig. 4. Variation of surface microhardness (H~) of Armco iron (1) and steel 1KhlSNIOT (2) dm~ing tests in tap water (dashed lines) and lime water (solid lines) with abrasive. when the energy of impact of the hydroabrasive stream increases sharply, the films are destroyed, and therefore the loss of mass is almost identical in lime water and tap water (Fig. 2). The slightly higher loss of mass in lime water can be explained by the reduction of the surface energy under the influence of adsorbed OH ions. This is confirmed by changes in the microhardness of Armco iron and steel IKhlSNIOT during tests in tap water and lime water (Fig. 4). The stage of plastic and plastic-destructive deformation of these metals lasts 40-80 sec from the beginning of the test. Dislocations and other defects occurring in this stage form pile-ups, develop into microeracks, and crystalline blocks are broken up, with an increase of the rater,hardness to the "limit" of strain hardening, which is higher in tap water than in lime water~ Then the surface layer breaks down, with formation of wear products, while the rater.hardness remains practically unchanged. The substantial effect of the corrosion factor on the hydroabrasive wear of metals in alkaline media is also confirmed by the effect of temperature on the loss of mass (Table 2). It is well known [9, I0] that raising the temperature of the medium affects cavitation wear~ The greatest wear in a given medium is observed at a specific temperature (50~ in water, for example). This is explained by the change in the cavitation power of the fluid due to the lower solubility of gases in it and also by the increase in its own partial vapor pressure. Since cavitation failure is due mainly to the mechanical effect of the fluid, the change in its physical properties is mainly responsible for the change in the intensity of cavitation with increasing temperatures of the fluid. In hydroabrasive wear the metal is damaged by the abrasive particles, and therefore a change in the physical properties of the fluid with an increase of temperature (lowering of the viscosity and density) can lead only to a slight increase in the loss of mass, while the higher rate of chemical processes is the decisive factor. Oxygen hardly dissolves in alkaline media [II], and therefore the increase in the intensity of hydroabrasive wear with increasing temperature of the lime water is due mainly to the increase in the.activity of the fluid itself. The results of the experiments lead to the conclusion that the intensity of hydroabrasive wear depends not only on the mechanical properties of the metals but also their interaction with the medium and the nature of the interaction products. LITERATURE i.

2.

CITED

A. I. Nekoz and N. A. Sologub, Zavod. Lab., No. 6 (1968). S. P. Kozyrev, Hydroabrasive Wear of Metals during Cavitation [in Russian], Mashinostroenle (1966).

9 135

3. 4. 5. 6. 7. 8. 9. 10. 11.

136

Pumps, Catalog-Handbook [in Russian], Mashgiz (1960). V . N . Kizel'shtein, C h e m i s t r y in T r e a t m e n t of Metals [in Russian], Lenizdat (1966). V . V . Gerasimov et al., C o r r o s i o n and Irradiation [in Russian], Gosatomizdat (1963). A . V . Ratner and V. G. Zelenskii, E r o s i o n of Metals in T h e r m a l Power Equipment [in Russian], ]~nergiya (1966). A . I . Nekoz, G. A. P r e i s , and N. A. Sologub, Fiz.-Khim. Mekhan. Mat., No. 5 (1969). A . I . Nekoz et al., in: Increasing the Wear Resistance and Service Life of Machines [in Russian], No. 3, UkrNIINTI (1970). A . I . Frid, Izv. Vuzov SSSR, Aviatsionnaya Tekhnika, No. 1 (1963). A . S . Bebchuk, Akust. Zh., No. 1 (1957). V . B . Kogan, S. K. Ogorodnikov, and V. V. Kafarov, Handbook on Solubility [in Russian], Volo 2, Nauka (1969).