the influence of the external parameters in cavitation ... · then it is presented the influence of...

THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS” OF GALAŢIFASCICLE VIII, 2002, ISSN 1221-4590

TRIBOLOGY

25

THE INFLUENCE OF THE EXTERNAL PARAMETERSIN CAVITATION DESTRUCTION

Octavian Bologa

“Dunărea de Jos” University, Galaţi, [email protected]

ABSTRACTFirst part of the work presents the industrial tribosystems and the cavitation

tribomodels. Then it is presented the influence of some external parameters incavitation destruction, such as cavitation germs, temperature and work environmentpressure,environment chemical composition, fluid viscosity and air content. Hereare highlighted the constructive and exploitation parameters and are analysed theprotection systems as the tension’s part in cavitation destruction. It is presented theexperimental accomplishments on a cavitation tribomodel with impact liquid jet.

KEYWORDS: cavitation, germs, tensions, viscosity, temperature, pressure.

1. Generalities

The introduction proposal for tribomechanicsystem notion or tribosystem is made in [21], [7], andafterwards the notion is standardised in DIN 50320[79]. The works of professor dr. eng. I. Crudu whoapproaches this thematic, finalised in [15], allow athoroughgoing analysis and a systematic presentationof the tribological processes not only in the case ofwear out phenomena but also in the case of industrialtribological systems.

A tribosystem (Fig. 1) is considered to becontaining:- a fix triboelement 1,- a mobile triboelement 2, (solid or liquid),- a material which is interposed 3 (lubricant, abrasive)- work environment 4.

If it is considered the relative movement typebetween the two triboelements1 and 2 and thematerial’s nature which is interposed, than we candistinguish [16], [17], [18], [19], [20]:

-the tribosystems of sliding or rolling sliding TA,-tribosystems of rolling or sliding rolling TR,-abrasive tribosystems TZ- cavitation tribosystems TC.As it can be noticed in picture 1 the cavitation

tribosystems can be:- hydrodynamic cavitation tribomodels TCh,- vibration cavitation tribomodels TCv,- impact liquid jet tribomodels TCi.

The model of a tribosystem is namedtribomodel, and contains the same elements as thetribosystem which is symbolized, with the initials TC.The labs’ installations on which are mountedtribomodels permit the acceleration of the wear out

process and consequently the shortage of the testingtime. On the basis of many experiments’ data it canbe asserted that to every tribosystem type correspondsa given wear out law. The type of war out that appearsis determined by the nature of the prevalent process(mechanic, thermal, chemical). In the superficiallayers of the machine bodies that compound thetribosystem. The type of wear out depends as much ofthe work parameters (forces, speeds, materials) thanthe work environment (characterised by temperature,pressure, electrochemical drive).

Fig.1

In practice the length of exploiting atribosystem, in most of the cases, is dictated by theallowed wear out on the surfaces of the machinebodies and it is scarcely appreciated on themechanical output. The durability of a tribosystemdepends on the external parameters (construction andexploitation work environment), parameters of thesuperficial layer (micro geometry, metallurgicalcharacteristics) and the parameters of the tribosystem(size of the motion, the thickness or the disposedmaterial quantity, contact flow).


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The external parameters for a tribosystem butalso for a cavitation tribomodel TC are presented inthe table 1. This work proposes to realize an analysisof the reference literature regarding the influence ofthe external parameters in the destruction of differenttriboelements which functions in cavitational regimeand to present a series of experiments made on a TCitribomodel type within the testing laboratory of theMachine Design Department of “Dunarea de Jos”University of Galati.

Table 1Cavitation germsTemperaturePressureChemical compositionThe viscidity

Characteristicparameters of

workenvironment The air content

DimenssionsConstructiveparameters Shapes

Cinnemetical parametersEnergetical parametersProtection systmes

EX

PL

OIT

AT

ION

PA

RA

ME

TE

RS

Exploitationparameters External loading

2. The influence of the work environmentparameters in cavitation destructions

Cavitation germsTheoretically, the cavitation appears in liquid

when the pressure becomes inferior to pressure pV, forthe ambient temperature. In reality, cavitation starts ata lower pressure, even to a higher pressure than theone of the saturated vapours. If it is considered thepure water in state of rest, the cavitation bulls appearby tensioning the liquid (lowering the pressure) whenthe pressure becomes equal to pV; if it is consideredthe impure water the phenomenon appears earliereven if p>pV. One of the main problems concerningthe appearance of cavitation is establishing theincipient pressure of cavitation, direction in which aremany theoretical and experimental researches [31].

Thus, it is wanted the complete or partialavoiding of cavitation initiation to reduce as much aspossible the destructive effects of cavitational erosion.The cavitation nuclear can be explained consideringthe non-uniform molecular structure of water. Thedifferent liquid molecules are distributed non-homogeneously; the distance between them is notconstant, and the reciprocal attractions are not thesame in all directions. Thus, in the liquid mass thereexist zones or void points, non-dissolved gas and solidparticles. The free gas is collected in tiny bags withinthe liquid mass and the impurities, by the nature oftheir material, or because of their shapes, is notcompletely wet and allows the formation of adherentbags filled up with gas, attached to these. All thesebags constitute incipient germs of cavitation. Thecavitation initiation can be homogenous orheterogeneous [3], [4].

The homogenous initiation acts in pure liquids,because of perturbations caused by molecular staticfluctuations of the local density while theheterogeneous nuclear acts at liquid – solid interfaces,so on impurities or at walls that surround the liquid.Thoroughgoing studies of the nuclear centre’sfunctioning on different forms are in [16], [17], [18],[19], [20], [21]. There have been determined: theinput depth, the transmission frequency of the centre,the bull’s diameter of detachment, the ascendingspeed of the bull.

The temperature influenceThe researchers that studied the influence of

the temperature on the cavitation destructions [59],have shown that the speed of destruction increases atthe start, passes through maximum and than drops tozero. Figure 2 presents the results obtained on atribomodel TCv for aluminium and copper alloys.

The law of desctruction speed at lowertemperatures is applied as the vaporisation pressure isrelatively small and the gas content that contributes tohe weakening of cavitation schock, is relatively high.

Fig.2


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Whem temperature grows, the dissolved gassvolume in liquid, diminishes, the vaporisationpressure increases and due to this fact, the effectcaused by the implosion of cavitation bubbles, alsobecomes greater. When continously increasing thefree gas temperature, a cushion pad has an importantrole in ameliorating the cavitation shocks. Thedestruction intensity weakens in these conditions.

The pressure influenceThe cavitational flows are characterised in an

usual way by the cavitation mark, through therelation:

20,5vp p

v

−σ =

ρ (1)

where: p and v are pressure and speed within a freecurrent. The cavitation experiments are usually doneby keeping constant the current speed and varying thepressure.

Holl [33], making tests on a tribomodel of TChand varying the flow regimes, noticed that there is apressures domain for which the flow has limitedcavitation. The limited cavitation can be obtained intwo ways: starting from cavitational flow, increasingthe pressure until reaching the pr value (remanentpressure) when the cavitation disappears; startingfrom non-cavitational flow, decreasing the pressureuntil it reaches pi value (incipient pressure) and thecavitation is produced. It was noticed that when pi < pr

and that there is a delayed time of cavitation’sappearance, after which the phenomenon is suddenlyproduced. Reaching the pressure pr is perfectlyreproducible whereas the incipient pressure varietieson a large scale. The stress values of incipient andremanent cavitation were defined as [37]:

20,5i vp p

v

−σ =

ρ;

20,5r vp p

v

−σ =

ρ (2)

The phenomenon was called cavitationhysteresis. Its measure is the delayed time ofcavitation appearance. The cavitation hysteresis is arelative phenomenon depending on the way offlowing and the surface characteristics. Oerkeny [56],for the tribomodels Tcv type indicates hanging of thecavitational cloud once with the changing of workpressure, without justifying this and without making aconnection with the possibility of cavitation hysteresisexistence at this type of tribomodels.

The pressure influence on tribomodels TCh isstudied by Koveney, Black, Johnson, and Maurer,referred in [61]. The interdependence between themass loss and pressure is shown in picture 3 fortribomodels TCv, and the pressure influence is shownin figure 4, researches in this direction being made byDeiley and Frank, mentioned in [61].Young and Johnson [77] studied the pressure’sinfluence on cavitational destructions in a tribomodelTCv type, the work environment being liquid Na. Itcan be observed that pressure’s increase leads to the

increase of mass loss. The pressure influence inbronze destruction SAE 660 is studied by Hammit[27], [28], who noticed that when the pressureincreases, the destruction increases too.

Fig.3 Fig.4

Chemical compositionAn important role in the cavitation destruction

process is played by the environmental chemicalcomposition. It was noticed that [23] the steel’sdestruction speed in 3% NaCl solution is three timebigger than the distilled water.

The cavitational corrosion in liquids, othersthan water, has a special practical interest, in relationto use organic substances and liquid metals as a workenvironment in pumps and turbines. It was studied thematerials behaviour, in their cavitational destructionsin toluene, ethanol, acetone, engine benzene, bearingoil, alkaline metals [61].

From the researches on cavitational corrosionmechanism [23], it results that material destruction isproduced by the help of some electro-, chemical,thermal, thermoelectrical phenomena, linked to thechemical composition of the environment. These non-mechanical factors can mainly speed up thedestruction process. Plesset [60] shows that a greatpart in the destruction intensification is played by thechemical and electrochemical interactions betweenthe metal and the work environment. The effect of thejoint action is much greater than the sum ofindependent action of cavitation and corrosion.

When using aggressive liquids in cavitationtribomodels, the corrosion influence is important.Steller [66] tested a set of different metallic materialson a tribomodel TCv in fresh water and salt water.The test results are presented in figure 5. The influen-ce of different liquids on the cavitation destructionprocess was studied by Piltz [61] and Schulmeister[67] on tribomodels TCv. By adding to Na, Ca andMg chloride and sulphide, in distilled water, Piltzshowed that the destruction speed of grey cast ironsamples increases with the liquid concentration.

The influence of chlorine ions on thedestruction is presented in figure 6. The developmentof corrosion process depends on the water hardnessmeasured by the Ca and Mg salts content, dissolved inwater. Figure 7 presents the dependency between themass loss speed, temper and temperature of water (forthe grey cast iron), the tests being made on atribomodel TCv [59].


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Fig.5 Fig.6

Fig.7 Fig.8

The changing of the environment compositioncan determine corrosion and thereby increase thedestruction or it can slow down the corrosion andthereby decreases the destruction. In figure 8 there areshown Schulmeister’s test results on grey cast irontest piece with the following composition: 3%C,0.6%Mn, 1%Si, and 0.3% P with a HV=210daN/mm2.

In order to emphasise the corrosion influenceon the cavitational erosion, Plesset [60] used theintermittent method. This method consists of exposingthe test pieces to the intermittent cavitational action

(after a period of exposure to cavitation it follows astationary period when the tests pieces remain sank inthe work liquid).

Nemecek [48] used tests with continue tointermittent cavitation and showed that the corrosionparticipation in the destruction process of carbonsteels leads to the destruction increase with a 65%,and in the case of alloyed steels (18% Cr, 8%Ni) with10%.Wide researches regarding the corrosion influence inthe cavitational destruction process are made byKuzman [42]. The tests were made in: water liquidNaCl, water liquid Na2So4, NaOH, acetic acid,preventol, furfurol, formaldehyde. The tests weremade on tribomodels TCv type at a frequency ofvibration of 7 KHz with double amplitude equal to94µm, at the temperature of 20 Celsius degrees andatmospherical pressure. It can be drawn theconclusion that once with the concentration increasegrows the cavitational destruction and than, at higherconcentrations it decreases. The results of some testsare presented in figure 9 and 10.

Okada [54], [55] studies the behaviour of highalloyed WC – CO (with 15.5 and 6 %Co) on atribomodel TCv in water and liquids of HNO3. NaOH,NaCl. It is noticed that deterioration due to cavitationincreases relatively slow when the cavitation actionintensity increase. Supplementary data referring to thecorrosion influence in cavitational destruction arefound in the paper [47]

Fig.9 Fig.10

Fig.11 Fig.12


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The viscosity influenceThe liquid viscosity influence on the cavita-

tional erosion was researched by Kozirev [39]. On theobtained results he established a relation betweenmass loss ∆m and the cinematic viscosity as follows:

bm a= +

ν (3)

where a, b are experimental constants.The relative influence of viscidity in cavitatio-

nal destruction of stainless steel (0.06%C+18.03%Cr+9.85%Ni+1.40%Si+1.37%Mn+2.16%Mo+0.09%S+0.026% P) was discussed and in [42].

The air contentUsing a tribomodel TCh Hansen studies the

behaviour of some triboelements from aluminium, fordifferent air quantities contained in the workenvironment (tap water and distilled water).

In figure 11 it is presented the influence of theair content for tap and distilled water in thecavitational destruction. The Co2 content influencesthe cavitational destruction at a higher content of0.55cm3/cm3, but not observing the destruction (figure12). On tribomodels TCv, Singer [68] obtains thebows of the destruction kinetic process fortriboelements of pure copper by varying the aircontent in the work water.

Fig.11 Fig.12

3. Constructive parameters incavitational tribomodels

The dimensions and the shapes oftriboelements in cavitational tribomodels have a greatdiversity. Thus, for tribomodel TCh Robinson uses apalette with grinded surface, placed in a workroomVenturi type of plexiglass (figure 13).

On a same kind tribomodel, Syamala Rao [69]tests triboelements placed in a workroom endowedwith a transparent cover. The studied triboelementlike a plate, is placed behind a cylindrical cavitationdriver. In the paper [72] Veerabhadra Rao uses atribomodel TCh with cylindrical samples placed on acircle with constant diameter (picture 14). Thetribomodels TCh type have been used for materialtesting also in [27].

Janakiram used a tribomodel TCi withrotational cylindrical samples and fix jets (figure 15a).In [69], Janakiram and Syamala Rao used a

tribomodel TCi with fix nozzles and mobilecylindrical samples (figure 15b).

Fig.13

Fig.14

Fig.15

Fig.16

Steller [66] uses triboelements with the form ofa cylindrical beak shape on tribomodel TCi. Diverse


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constructive shapes for models TCi are also presentedin works [17], [18], [19], [20], [3], [4]. For testing ontribomodels TCv in [14], it is presented an installationof magnetostriction with vibration nickel tube (picture16). Kuzman [42], uses threaded cylindrical samples,on a similar tribomodel (figure 16).

4. Exploitation parameters

Cinematic parametersFigure 17 presents Varga and Sebestyen’s

results regarding the influence of liquid flow speed onthe mass losses in a tribomodel TCh. The researcheshave confirmed the fact previously noticed that ∆m =f(vn). After analysis made by these researchers, thevalue of n exponent can vary between 4 and 8, andafter [37] has the value of n = 361 – 2.10 – 5N (N is theimpact number on TCi tribomodel). Eisenberg [23],was systematising the results of several researchers,showing that the modification of liquid flow speedmodified the intensity of cavitational erosion.

Fig.17

For tribomodels TCv, Gould [26] indicates theinfluence of the vibration amplitude on the mass loss(figure 18). Weiser studies the vibration frequencyinfluence upon the mass loss on tribomodels TCv, indistilled water (picture 19).

Fig.18

Protection systems

To minimise the corrosion effect in cavitationdestruction of metals, it is used: corrosion inhibitors,protection coats, cathode protection. Eisenberg [23],on a tribomodel TCv, tests steels grade 1020, with andwithout cathode protection, the results beingpresented in figure 20. Plesset [60], [61] has studied

closely the role of cathode protection in cavitationdestruction. In figure 21 it is presented the variationof mass loss for steel tribomodels, having a hardnessof 160 HV, for different intensities of the protectioncurrent, work environment being 3%NaCl solutionwith distilled water. Weiser studies the corrosioninhibitor influence. The protection coats of artificialresins are studied on tribomodels TCv and TCh bySteller [66]. Dorfman studies the metallic protectioncoats, made of Al, Zn and an alloy with Zn – 15%Alcoat applied by plasma spraying.

Fig.19

Fig.20 Fig.21

External tensions

Okada and Iwai [55] study the effect ofexternal loads on the cavitation destructions. Theyimagined a tribomodel TCv on a fatigue-testingmachine in a corrosive environment Shenk type andstudy the steel tribomodels SS41 and HT60 subduedto static and variable-compression stretch testing. Thetriboelements are under the form of plates of 3.5mmthickness, the surfaces being grinded.

The mass losses and the erosion speed fordifferent tests with SS41 steel (equivalent to AISIcontaining 0.13%C+0.0266%Si+0.44%Mn+0.012P+0.026% S) are presented in figure 22 and 23.

Fig. 22 Fig. 23


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Fig.24

Errdman and Tai [70], on a tribomodel TChtype, studies the static tension influence in cavitationdestruction, the test results for G-X6 CrNiMo 1810steel being presented in picture 24.

The researchers consider that the mechanicaltensions intensify the cavitational erosion, allowingthe formation of a great number of cavitation craters.Within the incubation period the mechanical tensionaccelerates the process of crazing grow. Similar dataare presented also in the works [4], [37], [661

5.Cavitation tribomodel with impactliquid jet, in open circuit

The tribomodel’s functioning is based on themodel proposed by Kozirev [24], the triboelement’ssurface destruction being produced by an intermittentshock between these and a liquid jet. The tribomodelis compound of a system with six cylindrical tubesfixed horizontally on the shaft, which is rotated with avariable revolution by a continuos current engine(picture 25). The water supply of the tubes is madeby in interior of the shaft, with the help of spiralpalette, tie-in on the shaft. The water jets that startfrom the nozzles are crossed by four cylindricaltriboelements, fixed on a disk, which spins backwardsthan the nozzles.

Fig. 25

The disk is driven by an asynchronous electricengine, through a multiplication system with trape-zoid belts, reaching a revolution speed of 3400rot/min

(figure 26). The revolution variation of the continuoscurrent engine in the range 0–2200rot/min, realisedwith a system of electronic thyristors.

Fig. 26

In order to determine the impact speed of thetriboelement and liquid jet, it will be analysed themovement of the carrying nozzle tube which rotateshorizontally with the angular speed ω (figure 27).The movement equation of mass liquid particle m iswritten with the formula:

ctcr FFNNgmam ++++= 1 (4)

which is reduced to: 02 =− xx ω!! (5)

with the solution of : tt eCeCx ωω21 += (6)

Fig. 27

(6) is derived and it is obtained :tt eCeCx ωω −−= 21! (7)

from the condition : 00 ==→= xandkxt ! , there

is determined C1=C2=k/2 .Taking into account that the time t=t1 the

particle leaves the nozzle, and it can be written:

2;

2

1111

2

tttt eekv

eekl

ωωωω

ω−− −=+= (8)


TRIBOLOGY

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Eliminating t1 from the relation (8), it is obtained :22

2 klv −=ω (9)

Knowing that lv ω=1 and that the

triboelement is rotated contrary to the angle speed

1ω , it can be calculated the total impact speed :

2

1

2

1 22

−++

=

l

klv

ωω

ωωω (10)

The attack angle will have the value of :'

'1 20 2 1

2

:v v

arctg where v lv

+α = = ω ⋅ (11)

The installation allows the modification oftriboelements position against the impact jet, and so itcan be obtained impact angles ∝ different than theattack angle ∝ 0, angles that are convenient for anexperiment planning having many impact speeds v.

6. Experiments planning on cavitationtribomodel with impact liquid jet

The arrangement of triboelements ontribomodel is presented in figure 28. The angularspeed of branches carrying nozzle could be varied inthe range 26-157 rad/s, the sizes of the commandparameters vary in a wide field. Within this domainthere were chosen two fix angular speeds ω forwhich there were made sets of experiments A, B, thevalues of characteristic elements being presented intable 2. Each set of experiments includes two specificexperiments for two values of impact angle ∝ . It isnoticed that by a convenient choosing of the reposeangle β, the impact angles for experiments sets A andB have smaller deviations than 0.40 .

To modify the angle β, the distance l1 betweenthe nozzle and the edge of triboelement, it will beused the relation:

1 0 0,5 costl l d= − βTo eliminate this modification there were used

calibrated separator collars (gs as thickness) whenassembling the nozzle with branch carrying nozzle,so, by adding them, the distance l1gor will be constantwith the value of 2 mm with maximum deviation of

0,05mm± . The parameters that can be varied intesting on tribomodel TC3 are: the impact speed v,impact angle ∝ and the nozzle diameter d0.

Fig. 28

Notes:

0α – attack angle;

β - repose angle,

α - impact angle,

1v – peripheral speed of triboelement,'2v – the total projection of the jet on the way of

triboelement movement.

7. Experiments

As appreciation markers of cavitationdestruction can be used mass loss ( )m f t∆ = or the b

mass loss intensity ( )mf t

t

δ∆ =∆

, accepted for mate-

rial behaviour characterisation to cavitation destruc-tion by the majority of the researchers. The mass lossvalues ∆m [mg], of different mass losses δ∆m[mg]

and of the wear intensity m

t

δ∆∆

[mg/min] are

presented in tables 3 and 4 for a jet with a diameter ofd0=4mm. In this case there were used triboelementswith the diameter of dt=16mm, parameters whichwere varied, given the impact angle α and the impactspeed v. The parameters of mass losses and of wear(or wear speed), are called kinetic parameters ofdestruction and are presented in figures 29-32.

For a jet with the diameter do=2mm, the valuesof mass losses ∆m [mg], of different mass losses δ∆m

[mg] and of the wear out speed m

t

δ∆∆

[mg/min] are

presented in table 5. In this case there were usedtriboelements with the diameter of dt=16mm, theparameter being the impact angle α. The values ofmass losses and of wear speed are presented in figures33 and 34.

Table 2Exp.

ω[rad/sec]

V1

[m/s]V2

[m/s]V[m/s]

Frd0 =2.5

Frd0 =4

0α[ 0 ]

β[ 0 ]

α[ 0 ]

l[mm]

gs

[mm]l1cor

[mm]

-5 72.5 2.03 0 2.03A100 11.5 11.22

51.98≅ 52 5133 3208 77.5 -15 92.5 2.27 0.3 1.97

0 72.9 2.00 0 2.00B157 18 18

59.96≅ 60 12659 7920 72.9 +20 92.9 2.48 0.5 1.98


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Table 3V= 60 m/s ; d0 = 4 mm ; dt=16 mm

α =72.50 ; β =00 α =92.50 ; β =200

Nr. Time

[min]

m∆

[mg]

mδ∆

[mg]

m

t

δ∆∆

minmg

m∆

[mg]

mδ∆

[mg]

m

t

δ∆∆

minmg

1 15 11.6 11.6 0.773 15.50 15.5 1.0332 30 18.95 7.35 0.490 25.90 10.4 0.6953 45 21.70 2.75 0.183 31.25 5.35 0.3564 60 26.50 5.20 0.347 37.90 6.65 0.4435 75 40.30 13.4 0.933 55.90 18.0 1.206 90 46.65 6.35 0.423 62.60 6.70 0.4467 105 54.00 7.35 0.490 66.70 4.10 0.2738 120 68.30 14.3 0.953 70.20 3.50 0.2339 135 90.30 22.0 1.466 76.10 5.90 0.39310 150 114.3 24.0 1.600 102.8 26.7 1.78011 165 122.9 8.60 0.575 108.95 6.15 0.41012 180 138.1 16.2 1.013 112.25 3.30 0.220


α =72.50 ; β =50 α =92.50 ; β =150

Nr. Time

[min

m∆

[mg]

mδ∆

[mg]

m

t

δ∆∆

minmg

m∆

[mg]

mδ∆

[mg]

m

t

δ∆∆

minmg

1 15 2.85 2.85 0.190 6.10 6.10 0.4062 30 10.45 7.68 0.505 18.40 12.30 0.8203 45 22.35 11.90 0.792 23.40 5.00 0.3334 60 31.85 9.50 0.630 26.80 3.40 0.2265 75 36.20 4.35 0.290 30.00 3.20 0.2136 90 38.10 1.90 0.125 35.40 5.40 0.3617 105 42.60 4.50 0.300 43.90 8.50 0.5678 120 52.80 10.20 0.680 65.10 21.20 1.4139 135 73.10 20.30 1.350 77.30 12.20 0.81310 150 91.10 18.00 1.200 85.70 8.40 0.56011 165 98.00 6.90 0.460 91.70 6.00 0.40012 180 102.4 4.40 0.290 94.40 2.70 0.180

168.704

0.176

f x( )

Y

f 1 x( )

VIT

1800.2 x X1, x, X1,0.1 1 10 100 1 10

30

50

100

150

200

trace 1trace 2trace 3trace 4

Time [min]

Des

truc

tion

spee

d x

100

[m

g/m

in]

Trace1 - ( )m f t∆ =

Trace 2 – experimental items

Trace 3 - ( )mf t

t

δ∆ =∆


d0=4mm dt=16mm

v=60m/s α = 72,50

Fig. 29


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178.32

25.71

f x( )

Y

f 1 x( )

VIT

1800.2 x X1, x, X1,0.1 1 10 100 1 10

350

0

50

100

150

200


Time [min]

Des

truc

tion

spee

d x

100

[m

g/m

in] Trace1 - ( )m f t∆ =


Trace 3 - ( )mf t

t

δ∆ =∆


d0=4mm dt=16mm

v=60m/s α = 92,50

Fig. 30

141.178150

0.013

f x( )

Y

f 1 x( )

VIT

1800.2 x X1, x, X1,0.1 1 10 100 1 10

30

50

100


Time [min]

Des

truc

tion

spee

d x

100

[m

g/m

in]


Trace 2– experimental items

Trace 3 - ( )mf t

t

δ∆ =∆


d0=4mm dt=16mm

v=52m/s α = 72,50

Fig. 30

141.776

0.596

f x( )

Y

f 1 x( )

VIT

1800.2 x X1, x, X1,0.1 1 10 100 1 10

350

0

50

100

150


Time [min]

Des

truc

tion

spee

d x

100

[m

g/m

in]



Trace 3 - ( )mf t

t

δ∆ =∆


d0=4mm dt=16mm

v=52m/s α = 92,50

Fig. 31


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α =72.50 ; β =00 α =92.50 ; β =200

No. Time

[min]

m∆

[mg]

mδ∆

[mg]

m

t

δ∆∆

minmg

m∆

[mg]

mδ∆

[mg]

m

t

δ∆∆

minmg

1 30 0 0 0 0.5 0.5 0.0162 60 1.15 1.15 0.038 2.00 1.5 0.053 90 1.85 0.70 0.023 2.75 0.75 0.0254 150 2.85 1.00 0.016 4.15 1.40 0.0235 210 6.05 3.20 0.053 8.80 4.65 0.0776 240 7.55 1.50 0.025 10.20 1.40 0.023

wetes

7.55

1.324

f x( )

Y

f 1 x( )

VIT

2400.2 x X1, x, X1,0.1 1 10 100 1 10

35

0

5

10


Timp [min]

Vite

za x

100

[m

g/m

in]

Fig.33

10.2

0.378

f x( )

Y

f 1 x( )

VIT

2400.2 x X1, x, X1,0.1 1 10 100 1 10

35

0

5

10

15


Timp [min]

Vit

eza

x 10

0 [

mg/

min

]

Fig.34


Trace 2 – experimental items d0=2mm dt=16mm

Trace 3 - ( )mf t

t

δ∆ =∆

v=60m/s α = 72,50


8. Conclusions

Analysing the bows presented in this paper asll as the results of experimental planning with fourt levels, it can be drawn the further conclusions:

- the destruction is manifested as a cumulativecyclic phenomenon,

- as the impact speed decreases, the cyclicnumber is diminishing and the time ofincubation increases

- the decrease of the nozzle’s diameter has asconsequence the decrease of cyclic numbers

- the extreme local values of destruction cycles(the local minimum an maximum) gavegenerally an increasing tendency,

- the impact angle has a special influence onthe kinetics’ process of destruction regarding


Trace 2 – experimental items d0=2mm dt=16mm

Trace 3 - ( )mf t

t

δ∆ =∆

v=60m/s α = 92,50


the total quantity of eroded material and thelength of incubation period,

- the modification of nozzle’s diameter leadsto essential modifications of eroded materialquantity and of the numbers of destructioncycles

- although the maximum speeds of thedestruction cycles for an impact angle of92.50 are superior to the impact angle of72.50, it is noticed that the mass loss after180 minutes is higher for the impact angle of72.50. This fact is due to the partialattenuation periods are stronger to the testingfor impact angle of 92.50,

- the minimum incubation period correspondsto an impact angle of 92.50 , and when themodification of impact angle increases, ofthe incubation period is longer,


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- the impact angle modification leads to amarked appearance of the maximum wearspeed,

- the total mass loss varies a little for impactangles included within the gap 70 – 1100 ,but once with leaving this gap, the masslosses are decreased considerably.

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