1971 Truscott A literature survey on abrasive wear in hidraulic machinery

Prévia do material em texto

Wear - Elsevier Sequoii S.A., Lausanne - Printed in the Netherlands 29 
A LITERATURE SURVEY ON ABRASIVE WEAR IN HYDRAULIC 
MACHINERY* 
G. F. TRUSCOTT 
The Brirish Hydromechanics Research Association, Cranfield, Bedford (Gt. Britain) 
(Received September 29, 1971) 
SUMMARY 
The survey considers the factors affecting abrasive wear-the properties of 
the solid particles, the construction materials and the flow-and various types of 
wear. The main sources of information are from laboratory wear tests on materials 
and pumps, and from service experience on pumps and water-turbines. The effects 
of wear on performance and working life are also discussed. Finally, the main points 
emerging from the survey are listed. 
1, INTRODUCTION 
There is a growing demand for both pumps and water-turbines which have to 
deal with abrasive solids in suspension. This requirement may be either by design- 
as in pumps for sewage, dredging or any other solids transport application-or 
default, e.g. any scheme involving river, land-drainage or glacial waters. In either 
case, the resulting wear is an increasing problem, particularly with the trend to 
higher running speeds. 
This survey is intended to provide a better understanding of abrasive wear 
phenomena, and as an aid to the selection of materials. It must be stressed, however, 
that the survey has been limited to abrasive wear only; other important factors 
affecting the final material choice for any given application, such as corrosion and 
cavitation erosion, are not covered, except where these properties happen to be 
mentioned for comparison in a particular report. Also, only those aspects of machine 
design which affect wear are considered, rather than the more general solids-handling 
capability, e.g. max. size of solid to be passed. 
The amount of published information, covering the past 20 years or so, is not 
large-there are only 38 references-and nearly all the original work is from con- 
tinental sources. The data may be conveniently divided into 3 main groups, together 
with the more comprehensive and useful references, as follows: 
(a) Wear tests on materials-Wellinger’, Stauffer’ 
(b) Wear tests on pumps-Zarzycki3 
(c) Service experience on pumps-Bergeron4 on general solids-handling, 
* “This paper is based on TN.1079 of the same title which is available from The British Hydromechanics 
Research Association, Cranfield, Bedford, at f2.” 
Wear, 20 (1972) 
30 G. F. TRUSCO’l.7 
Welte5 on dredging, Warman on sands and gravel, Bezinge’ on pumped-storage; 
and Bovet’ and Kermabong on water-turbines. 
Some attempts at theoretical wear analysis have also been made, notably by 
Bergeroni”~“. Most of the service experience concerns pumps, but it seems likely 
that similar wear processes occur in both types of hydraulic machinery. Quantitative 
wear tests on pumps are few--only two Polish papers, and one Russian, have been 
discovered. 
The survey considers the factors affecting and types of wear, and then deals 
with each of these in more detail. Finally, the effects of wear on performance and 
working life are discussed. 
2. FACTORS AFFECTING AND TYPES OF WEAR 
Most of the references deal with these topics in varying detail. 
2.1. Basicfizctors affecting wear 
These are the various properties of: 
(1) Solid particles-hardness, size, form (i.e. sharpness), relative density, 
concentration’,2,4~5*10- 13. 
(2) Construction materials-composition. structure, hardness’ - 5,7 - ‘,’ 2 - 14. 
(3) Flow-speed, impact angle’~2~4-6.s.10.11.13. 
Only the more detailed references are listed above. 
2.2. Types of wear 
These are also discussed in many of the references. In the material tests, 
Wellinger’ distinguishes between sliding, “scouring” and jet impact (sand-blasting) 
wear. Stauffer2 suggests “grazing”(i.e. 0” impact angle) scouring abrasion predominates 
in hydraulic machines. In papers on wear analysis (see Section 2.3), both Bergeron’“,l 1 
and Bitter’ 5 also attempt to separate wear due to friction (or cutting) and impact 
(or deformation) ; Bergeron’ ’ suggests how this wear mechanism may account for 
the typical pitting (or “gouging”) type of surface damage encountered in practice. 
Service experience on pumps4,5 and water-turbines’,‘, and pump wear 
tests3,‘3,‘6-1g, all show typical wear patterns of impellers, runners and casings for 
various running times. Warman discusses the differences in wear pattern between 
his design of pump and the conventional, also mentioned by Warring” and Arnstein”. 
2.3. Wear theory 
Several authors’,2,‘3*22-25 give simple expressions, based on wear test results, 
for wear rate as a function of velocity, material hardness, grain size or solids con- 
centration. The one most often quoted is: 
wear u; (vel.) 
where the index n may vary depending on the material and other factors involved; 
the most common value appears to be 3 2,13,24*25. It should be noted that Wellinger’s 
sand-blasing tests’ and Goodwin’s “whirling-arm” tests23 were carried out under 
dry conditions; however, although absolute wear rates presumably will be higher 
than in a liquid, the relative rates should be similar. 
Wear, 20 (1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 31 
Some more detailed analysess~‘0,“~15 consider wear as affected by the forces 
and velocities acting on a particle in a liquid flow. Bovet’ states that wear CC “abrasive 
power”, Pf, of a particle impinging on a surface, and 
P 
f 
= PVP,-PJC3 
4 
where p = coefficient of friction between particle and surface, I/ = volume of particle, 
ps = density of particle, p 1 = density of liquid, c = velocity of particle, R, = radius of 
curvature of surface. 
In a much more involved analysis, but starting with the same basic assumption, 
Bergeron 1 l develops a complicated expression based on the statement : 
wear oc solid/liquid density difference x acceleration of main flow x coefficient 
of friction x thickness of particle layer x flow velocity. 
He thus takes account of the difference between the solid and liquid velocities. 
His previous paper” attempts to predict wear rates in similar pumps handling solids 
with varying properties, with simplified assumptions such as pure sliding of the 
particles over the surface, from the initial expression 
wear cc -‘g (P-p)d3p K 
where U = characteristic velocity of liquid, 
P = density of particles, 
p =density of liquid. 
d = diam. of particles (assumed spherical), 
D = characteristic dimension of machine, 
p = no. of particles/unit surface area, 
K = experimental coefficient depending on abrasive nature of particles. 
Bitter”, in a fundamental study of erosion phenomena-but strictly for dry con- 
ditions-gives expressions for “cutting” and “deformation” wear, also based on 
energy considerations and the type of material eroded, i.e. whether brittle or ductile. 
A few authors4*‘0*13*1Q also develop expressions for pump service life. Both 
Bak13 and Bergeron4*” consider this in terms of pump total head for given conditions 
(see Section 6.2). Vasiliev’p gives a somewhat involved method, based on statistical 
analysis of pump wear tests, to predict life based on a specified maximum permitted 
wear. 
It is perhaps debatable whether these more complex theories can be used to 
predict absolute wear rates with anycertainty; most involve empirical constants and 
other parameters difficult to determine for an actual machine. In fact, BergeronloT1 l 
admits that some of the assumptions made may be questionable. However, such 
theories are of some value in predicting likely trends in wear rates when only one or 
two of the relevant factors are altered, 
3. EFFECTS OF ABRASIVE PARTICLE PROPERTIES 
3.1. Hardness 
Both Wehinger’s’ and Stauffer’s’ laboratory tests show that, for metals in 
general, wear increases rapidly once the particle hardnessexceeds that of the metal 
Wear, 20 (1972) 
32 G. F. TRUSCOTT 
1.50 
1.25 
1.00 
9, 
% 
I- 0.75 
L 
3 
0.50 
Fig. 1. Effect of grain hardness of abrasive media on steels and Vulkollan from scouring-wear tests. Water; 
solids mixture ratio by vol. 1 :l, velocity of test specimen 6.4 m/set; the steel hardness range is shown 
cross-hatched. (H,. = 110 kg/mm’ for St37; H,.=750 kg/mm* for C 60H). (From Wellinger and Uetz’.) 
Fig. 2. Effect of blasting abrasive hardness on direct impact wear from plate tests. Curves for steels, rubber 
and cast basalt. The hardness ranges for St37 (& = 125 kg/mm’) and C 60H (Ifr = 830 kg/mm”) are shown 
cross-hatched. (From WeLinger and Uetz’.) 
lo 20 30 50 70 100 2CO300 5007001000 2CCO3000 
Vickers hardness of abrading media 
Fig. 3. Effect of Vicker’s Hardness of abrading media on resistance factor. 
50 
m&/kg 
40 
30 
al 
% 
L 20 
k 
g 10 
Vickers 0 
hardness : 115 
material: St37 C60H 
(From Stauffer’.) 
Fig. 4. Effect of grain form of abrasive on direct impact wear. Plate tests with blast pressure of 2 atmos.: 
blank area for rounded “shot”, shaded area for angular “shot” with 1.6 mm grain size and Vicker’s Hardness 
H,,z 720 kg/mm’ (From Wellinger and Uetz’.) 
Wear. 20 (1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 33 
for both scourmg and impact abrasion. Beyond this, the wear rate may become fairly 
constant, or even reduce, with increasing abrasive hardness. These effects are shown 
in Figs. 1, 2 and 3; note that wear rates may be expressed in a variety of ways, both 
absolute and relative. Stauffer notes that the wear resistance of a 13% Cr cast steel 
was only slightly better than that of the “unalloyed” reference steel, whereas it is 
usually considerably better in practice; he suggests this might have been due to the 
excessive hardness of the test abrasive. 
From tests with various grades of very fine sand (< 200 pm) under dry con- 
ditions, Goodwin et al. 23 found that erosion varied as (hardness)23, and depended 
on the amount of quartz present. 
Rubber behaviour is more difficult to compare on a relative “hardness” basis; 
both “Vulkollan” and Perbunan synthetic rubbers showed fairly constant scouring 
wear rates (Fig. l), but Perbunan behaved like the reference steels in the sand-blasting 
tests (Fig. 2)‘. For both scouring and direct-impact wear, “Vulkollan” gave much 
lower wear rates than the steels, except with the less hard abrasives; the other rubbers 
were also better under direct (i.e. 90’) impact. 
3.2. Grain size and form 
Many of the references2,4,5~‘1,13~17~18,25 state that, in general, the absolute 
wear rate increases with grain size and sharpness. Other authors’,24 state that wear cc 
size for sliding or “grazing” abrasion, but is independent of size for direct impact; 
Goodwin’s tests23 show that the erosion rate for impact abrasion becomes constant 
only above a certain grain size (about 50-100 pm depending on velocity). Stauffer2 
also states that the relative wear (compared to the reference steel) of metals decreases 
with increasing size, but gives no results. Bergeron l1 found, from tests on Al. Br. that 
wear cc (size)0.75, but states that for general application, wear cc size x function of 
coefficient of friction, densities, and size/surface curvature ratio. 
Wellinger’ shows the effects of particle shape on impact abrasion in Fig. 4 ; 
angular grains cause about twice the wear due to rounded ones. Goodwin23 also 
discusses erosiveness of particles, and defines a “shape factor”; he states that hardness 
and sharpness are interrelated. 
Wiedenroth’s wear tests17*18 on a small dredge pump impeller, using a lacquer- 
removal technique, show differences in the blade wear pattern depending on grain 
size (i.e. sand or gravel). 
For rubber linings, the size and shape effects are more critical than for metals. 
Most of the “service experience” papers on pumps mention some limitation; actual 
size limits, varying from l/16 in. (10 mesh) up to 2 in. are quoted in Refs. 6,24-27. Two 
Eastern European papers on pump wear tests state limits of 5-6 mm (about $ in.)12 
and 4 mm (5/32 in.)13. Other references4*5*20*28 merely state that the solids should 
not be large or sharp. The size limit depends largely on the types of abrasive and 
rubber. 
3.3 Mixture concentration and density 
There is surprisingly little quantitative information on the effect of solids 
concentration. It is generally accepted that wear increases with concentra- 
tionl,4,11,13,19,22,24,25. Some authors’3,XS consider this relationship to be direct. 
Bergeron , ” from tests on Al. Br., suggested this applies only to small amounts of 
Wear, 20 (1972) 
34 G. F. TRUSCOTT 
solids, but for larger values wear increases more slowly; his theory states that wear 
x no. of grains/unit surface area, i.e. dependent on concentration and flow pattern. 
Kozirev’s jet impact tests” show wear x concentration, up to 10% solids, for pure 
abrasion, but this no longer applies for combined cavitation/abrasion. From the 
only pump test to consider this aspect, Vasiliev” concludes that wear x (concn.)“.x2. 
independent of material or flow properties, for sand/water mixtures between 3 and 
150/, by vol. 
Wellinger’ gives sliding-wear results for water/sand ratios from 0 to I; 1 ; 
his scouring-wear tests were carried out with a constant l/l sand/water mixture 
by vol., whereas Stauffe? used a 2/l mixture. For the Polish pump tests, Bak’” 
mentions a l/3 sand/water ratio, but no figure is quoted by Zarzycki3. 
Both Bovet8 and Bergeronr”,” give expressions (see Section 2.3) for wear 
depending on the density difference between solids and liquid, either varying direct- 
ly’-if other factors remain constant-or as a more complicated function”.’ ‘. 
4. EFFECTS OF CONSTRUCTION MATERIAL PROPERTIES 
4.1. Type : composition, structure 
4.1.1. Metals 
Wellinger’s material tests’ show that a hardened steel (C60H) had the highest 
resistance, followed by a hardened 13% Cr steel and an 18/8 stainless steel, to scouring 
wear (see Fig. 5). Hardened steel (St. 70H) and hard C.I. were better than the un- 
hardened reference steel (St. 37) for grazing abrasion, but worse for direct impact. 
under sand-blasting, as shown in Fig. 8. 
Stauffer’ tested over 300 materials, and gives 9 tables of results, a selection of 
which are given in Table I, on a basis of “resistance factor”, R = (vol. wear of ref. steel)/ 
(vol. wear of test material). Of the forged steels, a 12.5% Cr oil-hardened steel was 
best (R =6.0), and of the cast steels, a 14% Cr, 1.5-2% Mn nitrided steel (R=2.5). 
followed by a 12% Mn hardened austenitic steel (R = 1.9) ; 18/8 austenitic steels were 
not very resistant (R about 1.5). “Ni-hard” gave the highest resistance (R = 6.0) of 
the cast irons, and the S.G. irons were better (R = 1.0-2.3) than ordinary C.I. (R = 
0.5-0.8). Almost all the non-ferrous metals had a lower resistance than the reference 
case-hardening steel (C15) ; only a titanium alloy equalled it. Tin bronzes generally 
had the highest values (R =0.74.8) of the cast copper alloys-slightly better than the 
aluminium bronzes (R=0.554.7). A 30”/; Ni/2.5% Al bronze gave the best result 
(R = 0.94) of the wrought alloys. The most wear-resistant materials of all were the 
sintered tungsten carbides (R values up to 170), followed by hard chromium plating 
(R= 11.&18.0) and the hard Co-Cr-W alloy weld materials (R=4.5-18.0). 
Leith and McIlquham2’ give tables of comparative cavitation and abrasive 
erosion test results, referring to Stauffer’s work. Al. Br. has relatively poor abrasion 
resistance, but is excellent against cavitation; a Mn stainless steel shows only fair 
abrasion resistance, but cavitation resistance is good. Hard Cr plating gives excellent 
resistance to both, provided surface preparation of the base metalis adequate. 
Shchelkanov’s report r4 on water-turbine steel tests states that microstructure 
and work-hardening ability affect wear resistance considerably, austenitic and 
martensitic steels being notably better than the ferritic. It recommends using low 
and medium (3.5-10.5%) Cr alloy hardening steels, though both these and hardened 
11.5% Ni alloy and tool steels gave good abrasion and cavitation resistance. Kozirev’s 
Wear. 20 (1972) 
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ABRASIVE WEAR IN HYDRAULIC MACHINERY 39 
Wear, 20 (1972) 
40 (;. F. TRUSCOT’I 
jet-impact tests”, under both pure abrasion and combined cavitation/abrasion, 
showed an 18/S stainless steel to be more resistant than a case-hardening steel, cast 
iron and brass. 
Goodwin’s testsz3 with very tine, dry sand show that an il”,c Cr steel and a 
Cu-Cr---Ni alloy gave the same erosion rate-appreciably lower than for titanium 
and aluminium alloys. Antunes and Youlden25 give a table of results for a limited 
number of materials from mechanical grinding tests. 
The two Polish pump wear reports3Ti3 give generally similar results; of the 31 
materials tested by Zarzycki3 (see Table II) the 14:; and 4”//, Cr cast iron impellers 
had the highest wear resistance, followed by the 18-230.{ Cr and 12% Mn cast steels; 
S.G. cast iron was also quite good. 
Pump service experience may be loosely divided into dredging, sand and 
gravel, and slurries generally. Two German authors5*28 recommend either Mn or 
Ni-Cr-Mo-V cast steel for impellers and casing liners, with impeller sealing-rings 
of 30% Cr steel, for dredge pumps. “N&hard” (Ni-Cr white C.I.) and high Cr cast 
irons-for better corrosion resistance2’--appear to be the most commonly used for 
general solids-handling duties4.6,20,“,‘h.?7,30~3’, although Bergeron* states that, 
whilst ‘“Ni-hard” is very resistant to sharp abrasives, it tends to be brittle and hence 
prone to shock damage, so is unsuitable for dredge pumps. He also says that the high 
Mn steels, being work-hardened by impact, give good resistance against large, 
rounded solids, but are not much better than unalloyed steels against sand; some of 
the Ni-Cr-Mo alloy steels are very resistant to friction wear, but not to “saltating” 
(bouncing) particles. A good stainless steel may be used for resistance to erosion and 
corrosion. However, both Allis-Chalmer?’ and Warman pumps use “Ni-hard” 
for impellers handling coarse abrasives (Simonacco-Warman catalogue claims up to 
7.5 in. diam. for an 8 in. pump) ; both also use high Cr cast iron (27:/i Cr C.I. from 
Simonacco-Warman catalogue). Ref. 26 briefly mentions the use of hard-facing Cr 
or Ni alloys by welding, electrodeposition or metal spraying. 
Several references 7-9, 32, 33 relate to experience with hydroelectric plant. Be- 
zinge’ mentions improvements in storage pump wear by replacing impellers and 
casings originally in 13 “::, Cr,/l y<; Ni stainless steel by 13 “/c Cr/4% Ni. Stauffer”’ 
states a preference for cast steel with I2- i 4 ‘!,; Cr, up to 2.5 ?;;i, Ni, for water-turbines. 
However, Bovet*, discussing abrasive wear in all types of turbines, claims that the low 
alloy (1.5 0; Mn and 2 ‘!/; NQ0.7 % Mn) steels give as good an abrasion resistance as 
13 U< Cr stainless steel, which is much more expensive. Kermabon and Masse” also 
say that these low alloy steels are satisfactory. Both Bovet8 and Kermabon and Masse” 
give suitable materials for Pelton turbines-hard chrome weld overlay for needle 
valves, 18 p;; CrjI.8 “;; Mn stainless steel for nozzles8, or 13 ‘?g Cr high-carbon (1.552 I:$ 
forged steel for both valves and nozzles 9 ; for very abrasive duties, Cr-Ni-Mo steel 
for valvess, or 12--I 8 $4 W high-speed steels for valves and nozzles’. A 13 “/;: Cr/l.5 ‘:;I 
Ni cast steel is recommended’ for all types of turbine runners, having good cavitation 
resistance ; 18/8 stainless steel has rather poor abrasion, but good cavitation resistance. 
Of the non-ferrous alloys, the brasses and bronzes have poor wearing properties, but 
cupro-aluminium (9 Y/I Al) alloys are good,- also cavitation-resistant--and hence are 
also used for runners. Regarding surface coatings and weld overlays, metal-spraying 
with 1.2 “/( C steel--particularly on Pelton runners-gives good abrasion resistance, 
as does hard-chrome deposition on labyrinth seals. 
Weur, 20 (1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 41 
4.1.2. Rubbers 
There is a large variation in the wear rate depending on both type of rubber 
and abrasive, as shown by Wellinger’s tests’. The synthetic “Vulkollan E” (72” 
Shore H.) was the most resistant-better than the steels for the harder abrasives- 
but “Perbunan” rubber (88”-90” Shore) was much worse, in the scouring-wear tests. 
The sand-blast tests show, in Fig. 9, how wear depends on impact angle (see Section 
5.2.1.), with least relative wear occurring at 90”--opposite to that for steels; “Vulkol- 
lan” was better than the other rubbers, and all were better than the steels and C.I.‘s 
for direct impact. Stauffer’s tests’ gave very low resistance factors for rubbers, soft 
rubber (R = 0.08) being slightly better than hard (R = 0.05) ; he explains these results 
with reference to Wellinger’s. Bitter’s analysis ls also helps to explain this phenomenon. 
The rubber-coated impellers gave fairly good resistance-slightly inferior 
to high Mn alloy steel-in the Polish pump wear tests3,13. Russian tests12 on rubber 
coatings claim a much-improved resistance for natural and methylstyrene rubbers 
over that for the butadiene-styrene rubber previously used; isoprene rubber was 
also very promising. The report states that wear reduces with hardness for particles 
< 1 mm (0.04 in.), and with increasing tensile strength and elasticity for particles 
< 556 mm (about a in.) (See also Section 3.2.). 
Although most of the references4-6,20,21,24,26-28*30 on pump service ex- 
perience mention the greater wear resistance of rubber over metal, within the limits 
of particle size and form discussed in Section 3.2-also provided that operating 
temperatures are below about 130°-1600F2’,26, and the bonding is good4,12,26,28,30- 
there is relatively little information on the types of rubber used. Welte’ recommends 
rubber of 50”-65” Shore hardness for coating both impellers and casings, and 40”-60” 
Shore hardness for impeller and shaft seals, for dredge pumps. Again, Bergeron4 
suggests that rubber is unsuitable for such pumps, owing to the danger of impact 
from large solids. The article26 on slurry pumping states that natural and the softer 
synthetic rubbers are more wear-resistant than the semi-hard ones, but are not so 
corrosion-resistant. Egger’s paper3’ gives similar recommendations, soft rubber 
linings being most suitable for sand, quartz, kaolin and other abrasive slurries, 
whilst hard rubbers are for chemical applications ; “Vulkollan” impellers and sealing- 
rings gave the highest abrasion resistance-about twice that of a 16% Cr hard C.I. 
Kermabon and Mosseg briefly mention the satisfactory use of synthetic rubber in 
some water-turbine applications. 
4.1.3. Plastics 
There appears to be little published information so far on the use and behaviour 
of plastics. Wellingerl tested 3 plastics for scouring wear; “Lupolen H” (stabilized 
polyethylene) was best-better than “Perbunan” rubber, or about the same as 18/8 
stainless steel-but “Vinidur” (vinyl type) and “Polystyrol EH” (polystyrene) were 
much less resistant. Stauffer2 also tested several types, but all were much worse than 
steel ; polyethylene was again the best (R = 0.32), followed by “Nylon” and “Teflon” 
(R =0.28). “Perspex”, “ Bakelite” and other synthetic resins were poor (R = 0.04-0.07). 
However, two Russian papers34v3s report encouraging results from abrasion and 
cavitation tests on polyether and epoxy resins, and elastomers, but give few details, 
apart from stating that specimens were undamaged after 30 h; the resin materials 
included 2&40x by wt. of fillers (e.g. emery or granite powders, steel tilings) or 
Wear, 20 (1972) 
42 <;. F. TRUSCOTT 
glass-fibre reinforcement. They claim successful application to semi-open and axial 
pump impellers, anda Francis turbine runner and guide-vanes, under abrasive 
conditions. Goodwin’s tests23 with sand dust show that polypropylene had the 
highest resistance of the plastics, followed by glass-reinforced nylon-6,6, and libre- 
glass as a poor third; all were inferior to the metals. 
Epoxy resin impellers failed rapidly in Zarzycki’s pump tests3, and “Stilone” 
coating gave rather poor resistance. Discussion has revealed that some work has 
been done on polyurethane coatings for pumps, but no reports have been published 
and no commercial application in the U.K. has appeared so far. 
A review article” on solids-handling pumps mentions the use of polyethylene 
lining for paper-pulp duty. The Dutch Begemann Co. makes chemical pumps in 
reinforced epoxy resin (duties up to 300 ft head and 250”F), chlorinated polyether, 
PVC and polypropylene, but the abrasion resistance is not stated36. Kermabon and 
Masse’ report that plastics linings tried in water-turbines were not very satisfactory. 
4.1.4. Ceramics 
Once again there is very little information, and probably only limited applica- 
tion. Wellinger’s sand-blast and sliding wear (dry) tests’ showed that sintered corundum 
(Al oxide) had a very high wear resistance-no scouring wear results are given. 
Antunes and Youldenz5 include ceramics with rubbers in pump head and 
particle size (< $ in.) limitations. Warring’s review” states that silicon carbide has 
excellent abrasion and corrosion resistance, but is brittle, so has relatively limited 
application. Some Allis-Chalmers pumps use ceramic impeller sealing rings’ ‘. 
Gould Pumps Inc. claim to have developed a small all-ceramic pump in a special 
material (“Cer-Vit”) having negligible thermal expansion, hence capable of with- 
standing thermal shock; operating temperature is, however, limited to 350°F36. 
Ceramics are, of course, also used for mechanical seal faces3’ (see Section 
6.2.2.). 
4.2. Hardness 
In very general terms, the wear resistance of ferrous metals tends to increase 
with hardness’,2,‘4*29. Antunes and Youlden” state that “most tests” show an almost 
linear variation, but Stauffer* found no straightforward relation between them ; 
Bergeron4 also states that hardness is not a criterion of wear. Stauffer’s results show 
the general trend, but there is a large scatter, with some harder materials giving much 
lower resistance factors than the softer ones (see Table I). It may be noted, however, 
that the more wear-resistant materials, with R from 2.4 up to 170, had hardness 
values ranging from 600 to 2450 HV (Vickers Hardness). Even a trend does not appear 
to exist for the copper alloys; the resistance of tin bronzes is almost constant, in- 
dependent of hardness. Wellinger’ gives wear rates for a limited number of steels with 
a hardness range from 110 to 850 HV, from both scouring- and blasting-wear tests 
(see Figs. 5 and 6 respectively). The Russian paper14 on water-turbine steels re- 
commends hardness values of at least 375-400 HB (Brine11 Hardness), and also 
notes the increase in microhardness from 241 to 412 HB due to work-hardening of 
an austenitic steel. 
The hardness range of the impeller materials in Zarzycki’s pump tests3 varied 
from 80 to 540 HB; the most resistant (high Cr C.I.) had a hardness of 328 HB, 
Wear, ZO(1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 43 
Vickers hardness Hv 
80, , , I 
I LVickers l-wdn ” 
Material St37 !C6ohadened 
tempere 
%&A&/ mm2 
ess Hv : ; . I 
I and 
!d k” 
Fig. 5. Effect of steel hardness on scouring wear with quartz sand. Water/solids mixture ratio by vol. 
1 : 1; velocity of test specimen 6.4 m/set. (From Wellinger and Uetz’.) 
Fig. 6. Effect 01 material hardness on direct impact wear from plate tests. Blast pressure 3 atmos. (a) Curve 
for blasting with quartz sand (grain size 0.2-1.5 mm Vicker’s Hardness, H, = 1290 kg/mm’) ; (b) curve for 
blasting with cast “shot” no. 1 (l-l.5 mm, H,= 395-550 kg/mm*); (c) curve for blasting with cast “shot” 
no. 7 (1.6 mm H, = 69G750 kg/mm’). Hardness ranges of cast shots 1 and 7 shown cross-hatched. (From 
Wellinger and Uetz’.) 
whilst the next best (low Cr C.I.) had the much higher value of 516 HB, as shown in 
Table II. Bak’s results’3 were generally similar, though the most resistant materials 
(“Ni-hard” and high Cr C.I.) were, in fact, the hardest-about 800 HB. 
Such hardness values as are quoted for production pump materials vary from 
400 to 650 HB (“special” alloy steels) for American dredge pump liners38, 34CL450 
HB (Cr C.I.) for Allis-Chalmers pumps27, 550 HB (“N&hard”) for Warman pumps 
(from sales literature), and 25&700 HB for various European solids-handling pumps’ 3. 
The change in storage pump materials, which Bezinge7 mentions gave improved life, 
meant an increase in hardness range from 180 to 200 HB (13% Cr/l% Ni stainless 
steel) to 23&300 HB (13% Cr/4% Ni stainless steel); new labyrinth seal materials, 
either “specially treated” steel of 50&550 HB or hard-chrome deposition of 650-700 
HB are also being used. 
5. EFFECTS OF FLOW PROPERTIES 
5.1. Speed ; speed and head limits 
The more straightforward wear theoriess9r0 suggest that wear cc (ve1.)3, or cc 
(total head) 3’2 if all other factors are constant (see Section 2.3.) ; even Bergeron’s 
more complex expression’l, taking account of the difference in velocity between 
fluid and particle, gives a similar result, provided that the particle velocity is con- 
sidered. Bitter’s theory”, however, considers total wear as the sum of “deformation” 
and “cutting” erosion, both involving the material properties as well as speed, so 
that wear cannot be stated as a simple function of velocity. 
Material tests show some variation in the velocity index. Wellinger’s sand- 
blast tests’, shown in Fig. 10, indicate that it depends on the material-for steel 
(St. 37), the index is 1.4, and for rubber, 4.6. Stauffer’ found that wear approx. cc 
Wear, 20 (1972) 
44 G. F. TKUSCOT~I 
(vel.)3, as mentioned by Worsterz4, and Bergeron” suggests that the index is >i. 
Kozirev’s jet impact tests ** showed that, for constant mixture concentration and 
without cavitation, wear =c (vel.)2,2. GoodwinZ3 found that wear T/ (vcl.)‘.” for all 
materials tested (both metals and plastics) and for particle sizes > 125 /Lrn, under dry 
conditions and at relatively high speed (up to 1800 ft/sec). Antunes and Youlden”s 
conclude from wear literature that for ductile materials, wear approx. #x (vcl.)” if 
vel. < 100 ft/sec, or x (ve1.)2 if vel. > 100 ftisec; for brittle materials. the index may bc 
higher. 
Bak’s pump wear tests I3 also indicate that wear x (vel.)3; the other pump tests 
do not investigate this aspect. 
Many of the service experience references5*6.20.2’.25-28.38 on pumps give 
speed and/or head limitations. For dredge pumps, maximum impeller tip speeds vary 
from 70 to 150 ft/sec5.28,38 and maximum heads from 80 ft to nearly 300 ft5.28; the 
type of lining to which these limits apply is not stated specifically in Refs. 5 and 28 
but probably the lower limits refer to rubber. For metal-lined sands and slurry pumps, 
maximum heads quoted range from 160 to 200 ft/stage in genera120.2”, and with 
“Ni-hard” linings up to 260 ft for Warman “Series A” pumps (from selection chart)6, 
or 320 ft for Allis-Chalmers pumps2’. Rubber-lined pumps have much lower limits, 
e.g. 70 ft/sec maximum tip speed* ‘, and 90-I 50 ft maximum 12.13.20,21,25 head (120 ft 
for Wilkinson “Linatex” pumps*‘). Ceramic linings are also said to be unsuitable 
01 1 I i I I I 
0’ 30” 60” 900 
Implngement angle cx 
‘High-sp’eeki sieei 
Tooi steel &7() 
Impingement angle a 
I1 1 1 6 I I I 
6660 1100 900 785 583 624 y/h 
Wear rate V, for St 37 
Fig. 7. Blasting-wear rate for steel St37 plates. Sand-blasting tests by M. Gary. Blasting material: quartz 
sand of grain size 0.2-1.5 mm. V,, measuredblasting-wear rate; Vi= V,./sinx, specific blasting-wear rate. 
(From Wellinger and Uetz’.) 
Fig. 8. Blasting-wear/jet impingement angle diagram. Wear curves using quartz sand (grain size 0.2 --I .S mm). 
(From Wellinger and Uetz’.) 
Wrar. 20 (1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 45 
for high heads’ 5 ; the first of the new Gould range is designed for 60 ft head (140 ft 
at shut-valve) 36 Warman also states that a lower specific speed design for a given . 
duty results in reduced wear, although heavier and more costly, since lower peripheral 
speeds are involved compared to the higher N, alternative. 
5.2. Direction (impact angle) ; hydraulic design 
5.2.1. Impact angle 
Bovet’s theory8 results in wear depending on the tangential component of 
particle velocity, so that as the impact angle is increased wear is reduced. Bergeron’s 
simpler theory lo directly applies only to pure sliding (“friction”) wear, but the more 
complex onelr deals with the more general case of oblique impact (see Section 2.3). 
Bitter’s expressionsr5 for cutting and deformation wear imply that total wear depends 
on both normal and tangential velocity components. 
103 
102 
1 
0 
z 
L 
3 
lo’ 
IO0 
Impingement angle tx Air veloctty C 
z3v m/s 
Fig. 9. Blasting-wear/jet impingement angle diagram. Wear range of different material groups using 
quartz sand (grain size 0.2-1.5 mm). (From Wellinger and Uetz’.) 
Fig. 10. Effect of air velocity on direct impact wear. Plate tests with quartz sand (grain size 0.2-1.5 mm). 
m, curve slope. (From Wellinger and Uetz’.) 
Wear, 20 (1972) 
Wellinger’s sand-blasting tests’ show, in Figs. 7, 8 and 9, how the effect of 
impact angle depends on the type of material; for steels and CL’s, both absolute and 
relative wear rates tend to increase with angle, reaching a maximum between 60’ 
and 90”, whilst for rubbers the reverse is true (see Sections 4.1.1. and 4.1.2). Stauffer’, 
Wiedenroth18 and Welte’ all note Wellinger’s results; Antunes and Youlden’” also 
mention the impact angle effect. 
5.2.2. Hydraulic design 
The Polish pump wear tests3*i3 investigated different types of impellers. Both 
report slightly higher wear rates for a conventional “bladed” design than for an un- 
chokable “channel” type; Zarzycki3 gives results for both types in all materials, as 
well as for 2-bladed “propeller” designs-see Table II. Wiedenroth’s visual studies’ ‘gl 8 
from his lacquer-wear tests showed wear only on the suction side of the impeller 
blades when pumping sand, but extending to the pressure side with “line” gravel ; 
wear at the outlet tips increased with flow. Herbich’s reporti on dredge pump design 
mentions that least wear occurred for a blade outlet angle of 22.5”, over the range 
225-35” ; the exit angle of the solid particles then corresponded closely to the blade 
angle. 
Several authors4.5.‘3.18~25,28 stress the importance of maintaining good 
hydraulic design, as far as solids-handling considerations will allow, to minimize 
wear, and particularly avoiding rapid changes of direction4,5.‘8.25. There also seems 
to be a general preference for shrouded pump impellers, notably for dredging4,‘,’ 6.28 
though it has been suggested*’ that the choice between shrouded or open type depends 
on the solids being pumped. Welte ‘, discussing wear patterns in dredge pumps, 
states that wear is greatest at the impeller blade inlet and outlet edges, and on the 
outer shroud walls on the suction side; casing wear is usually greatest near the cut- 
water. Generally similar tendencies are noted by other authors3~4,‘3~‘7- 19. Both 
German dredge pump papers 5.28 show designs having a relatively small volute side 
clearance. However, Bergeron4, in discussing the effects of primary and secondary 
flow patterns on pump wear, recommends a large side clearance-except where 
scraper-vanes are used-as well as shrouded impellers and large radii of curvature. 
Regarding the less conventional pump types, Warman compares casing wear 
patterns using the conventional and his own design, and claims that wear is reduced 
with the latter’s special impeller shape. References 20 and 21 also mention this aspect. 
A few references20,30.31 discuss wear in torque-flow (or “free-flow”) pumps; Egger’s 
paper 3o also gives constructional details of “TURO” designs. Wear is stated to bc 
less of a problem in this type than the conventional*‘, but the only comparison 
reported31 involves a different construction material for each type. 
6. EFFECTS ON HYDRAULIC PERFORMANCE, WORKING LIFE AND SEALING 
6.1. Performance 
There is very little quantitative information available, and only on hydro- 
electric plant. Bezinge’ shows the effect on storage pump performance of worn 
labyrinth seal clearances. Ferry et al.33 discuss the reduction in efficiency due to 
increased clearances in Francis turbines, and worn nozzles and runners in Pelton 
machines. 
Wear, 20 (1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 47 
6.2. Life 
Expressions for predicting pump life are given in Refs. 4, 13 and 19. Both 
Bak13 and Bergeron4 state that, for pumps, 
‘lfe Oc (total lead)“/’ (i’e’ K weaf rate) 
Bak then gives a formula which includes the other factors affecting wear : 
life in h., T = A K Q" 
H312 WX s 
where A = constant factor, Q” = solids concentration in mixture, ‘/& K = impeller 
shape factor (1.0 for multi-bladed impellers, 1.4 for “channel” impellers), H = total 
head/stage, m.H,O, W,=coefficient of abrasive wear for impeller material, e.g. from 
Table II 
vol. wear of test material 
= = 
vol. wear of ref. material (C.I.) 
, X = coefficient of abrasiveness of 
solids. 
(Factor A is probably based on some known life figure, e.g. for coal pumps, AQ”= 
25,500 approx.). Bergeron4 also develops expressions for determining service lives of 
geometrically similar pumps of different size, in terms of head and flow variations. 
Vasiliev” analyzes the statistical probability of a pump achieving a certain length 
of “trouble-free” service, defined by a specified maximum wear, based on erosion 
tests. 
6.2.1. Metal vs. rubber lining ; impeller seals 
Many authors mention the longer life of rubber over metal linings, within the 
limitations previously discussed (see Sections 3.2. and 4.1.2.). Improvements by 
factors of 610 have been reported 28 for German dredge pumps, and 2.5-5 x life 
with “special” C.I. (or 2&30 x life with grey C.I.) for Russian solids-handling 
pumps l2 ; this Russian report also notes that the newer grades of rubber were 5-10 
times more resistant than the old. Welte’ states that the life of some dredgepump 
metal parts may be only 4&60 h, but improvements by factors of 3-10 have resulted 
from wear research, particularly on impeller seals-various designs are shown, all 
using rubber, with a clean water supply 5,28. The economic choice of materials depends 
on the ratio of (total cost)/(wear resistance). Bergeron4 also discussed possible 
impeller seal designs. 
A few references6*13,30,31 give life figures for specific solids-handling pump 
applications. Baki3 quotes some service lives from Continental experience, varying 
from 84 h for 25-30x Cr steel parts pumping sand, to 20,000 h for a similar steel with 
coal slurry. Warman also gives some life figures for casings and impellers when 
handling different abrasives. For torque-flow pumps, Egger3’ shows the variation of 
TURO-pump life with type of abrasive, for various construction materials. Rubber 
lining may reduce wear down to f of that for metals; “Vulkollan” had the highest 
resistance, and gave about twice the life for 16% Cr hard C.I. Grabow31 compares 
casing and impeller wear of a conventional Cr cast steel-lined pump with that of a 
torque-flow pump in “Ni-hard 4”, and notes about 50-80x improvement in life for 
the latter. 
Wear, 20 (1972) 
48c;. F. ‘TRUSC‘OTI 
Regarding hydroelectric machinery, Bezinge7 gives case histories of a number 
of pumped-storage schemes, with improvements in repair and maintenance schedules 
resulting from changes in materials and sand settling. Bovet’ and Kermabon and 
Masse’ both show wear patterns for different water-turbine materials after various 
running periods. 
6.2.2. Shuft sealing 
Many of the papers4-6~20~21~26~28 on solids-handling pumps make some 
reference to gland-sealing; for soft-packed glands, nearly all recommended either a 
grease or clean water supply, with or without scraper-vanes on the impeller, or the 
separate centrifugal seal suggested by Warman 6. The review article by Warring” 
gives a list of manufacturers using different seal types. 
There is not much information on the use of mechanical seals. Koch37 discusses 
their application for abrasive duties, investigates possible materials-including 
metallic carbides and oxides-design and cooling problems, and gives typical 
examples. Welte5 and Ernst’* show dredge p ump designs involving lip-seals, with 
clear water and/or grease supply. The slurry pump reviewz6 also mentioned the 
“Trist” seal as suitable, without separate flushing. 
7. MAIN POINTS EMERGING FROM THE SURVEY 
Owing to the large number of factors affecting abrasive wear, it does not appear 
possible to make just a few overall hard-and-fast rules as to the best way of reducing it ; 
each case will still have to be treated on its merits, not least of which must be economic. 
However, it is worth noting some general trends derived from the literature for the 
designer’s consideration. 
(1) Wear increases rapidly when the particle hardness exceeds that of the metal 
surface being abraded. 
(2) Wear increases generally with grain size, sharpness and solids concen- 
tration. Rubber lining is particularly vulnerable to large, sharp particles. 
(3) Metal hardness is not an absolute criteria of wear, although for ferrous 
metals, the expected trend for wear resistance to increase with hardness applies very 
generally. A reasonable resistance appears to be achieved above about 300 HB. The 
very hard alloys (e.g. tungsten carbide) and surface treatments are extremely resistant. 
(4) Chemical composition, microstructure and work-hardening ability all play 
an important part in wear resistance of metals. Austenitic Cr-Ni (12-14% Cr) and 
Mn alloy steels are good, as is “Ni-hard” (Ni-Cr) cast iron. 18/8 stainless steel (though 
resistant to cavitation) and most non-ferrous metals, except cupro-aluminium, 
have rather poor abrasion resistance. 
(5) Soft rubber appears generally more resistant than hard. 
(6) Plastics coatings do not appear very promising so far, except possibly in 
particular applications; bonding can also be a problem. Ceramics are very wear- 
resistant, but their use to date has been limited by brittleness and susceptibility to 
thermal shock. New developments in small pump applications may show improve- 
ments. 
(7) Wear increases rapidly with flow velocity, and is often reported as being 
approx. yc (velocity)3, or cc (pump head) 3/2 from both theoretical considerations and , 
Weur. 20 (1972) 
ABRASIVE WEAR IN HYDRAULIC MACHINERY 49 
test results. The actual value of the index, for any given conditions, probably depends 
on at least some, if not all, of the other factors involved in the overall wear process. 
Head limits quoted are up to about 300 ft/stage for all-metal pumps, and 
150 ft/stage for rubber-lined. 
(8) Impact angle has a marked effect on wear; metals and rubbers behave in 
opposite ways. 
(9) Good hydraulic design, particularly by avoiding rapid changes in flow 
direction, decreases wear, and should be compromised as little as possible by solids- 
handling considerations. Shrouded impellers are generally favoured. 
(10) Rubber lining can give a much-increased life compared to that for metal, 
provided that the solids are not large or sharp, bonding is good, and heads and 
temperatures relatively low. 
(11) Soft-packed shaft glands require a grease or clean water supply; scraper- 
vanes on the impeller, or separate centrifugal seals, are also used to protect the 
glands. Mechanical seals with special materials, and usually with a flushing supply, 
are sometimes fitted. 
(12) No outstanding new construction materials, suitable for commercial 
application to a wide range of machine sizes, have been reported to date. 
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50 c;. F. TRUSCOTI- 
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on Current operation-orientated research problems in hydraulic machines, Lausanne. 1968, Paper H2. 
11 PP. 
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