scientific problems of sciences of machines...

POLISH ACADEMY OF SCIENCES COMMITTEE OF MACHINE ENGINEERING

SCIENTIFIC PROBLEMS OF MACHINES OPERATIONAND MAINTENANCE

ZAGADNIENIA EKSPLOATACJI MASZYN

TRIBOLOGY • RELIABILITY • TEROTECHNOLOGY DIAGNOSTICS • SAFETY • ECO-ENGINEERING

TRIBOLOGIA • NIEZAWODNOŚĆ • EKSPLOATYKA

DIAGNOSTYKA • BEZPIECZEŃSTWO • EKOINŻYNIERIA

1 (161) Vol. 45

2010

Institute for Sustainable Technologies – National Research Institute, Radom

EDITORIAL BOARD:

Editor in Chief Stanisław Pytko Deputy Editor in Chief Marian Szczerek Editor of Tribology Marian Szczerek Editor of Reliability Janusz Szpytko Editor of Terotechnology Tomasz Nowakowski Editor of Diagnostics Wojciech Moczulski Editor of Safety Kazimierz Kosmowski Editor of Eco-Engineering Zbigniew Kłos Scientific Secretary Jan Szybka Secretary Ewa Szczepanik EDITORIAL ADVISORY BOARD Bolesław Wojciechowicz (Chairman) Alfred Brandowski, Tadeusz Burakowski, Czesław Cempel, Wojciech Cholewa, Zbigniew Dąbrowski, Jerzy Jaźwiński, Jan Kiciński, Ryszard Marczak, Adam Mazurkiewicz, Leszek Powierża, Tadeusz Szopa, Wiesław Zwierzycki, Bogdan Żółtowski and Michael J. Furey (USA), Anatolij Ryzhkin (Russia), Zhu Sheng (China), Gwidon Stachowiak (Australia), Vladas Vekteris (Lithuania).

Mailing address: Scientific Problems of Machines Operation and Maintenance Institute for Sustainable Technologies – National Research Institute ul. Pułaskiego 6/10, 26-600 Radom, Poland Phone (48-48) 364 47 90 E-mail: [email protected]

The figures have been directly reproduced from the originals submitted by the Authors.

Publishing House of Institute for Sustainable Technologies – National Research Institute 26-600 Radom, K. Pułaskiego 6/10 St., phone (48-48) 364-42-41, fax (048) 364-47-65

www.tribologia.org 2081

SCIENTIFIC PROBLEMS OF MACHINES OPERATION AND MAINTENANCE

1 (161) 2010

CONTENTS O. P. Parenago, G. N. Kuzmina, V. D. Terekhin, K. Yu. Basharina:

Antifriction and antiwear properties of molybdenum sulfides nanosized particles synthesized using nitrogen containing ionic liquids ............................................................................... 7

A. V. Rădulescu, I. Radulescu, C. Cristescu: Experimental study on

the rheological behavior of H46 lubricant oil ........................... 15 R. G. Ripeanu, I. Tudor, I. Zidaru, Adrian C. Drumeanu:

The lubricant and implants influence above tribological behaviour at three cone bits bearings ......................................... 25

Z. Rymuza: Advanced techniques for nanotribological studies ............. 33 Yu. P. Sharkeev, V. A Kukareko, E. V. Legostaeva, A. V. Byeli:

Nanostructured composite materials on the base of titanium and zirconium alloys with modified surface layers for medicine and engineering .......................................................... 45

S. Strzelecki, S. M. Ghoneam: The effect of clearance variation on the

maximum temperature of the oil film of cylindrical 3-lobe journal bearing ........................................................................... 52

K. Wierzcholski, A. Miszczak: Adhesion influence on the oil velocity

and friction forces in conical microbearing gap ......................... 61 K. Wierzcholski, A.Miszczak: Adhesion influence on the oil velocity

and friction forces in cylindrical microbearing gap .................. 71 N. V. Zaitseva, S. М. Zakharov, О. А. Shmatko, I. L. Oborskyi: The

influence of vibrating processing on a variation of the chemical composition and properties of electrospark mattings on steel ....................................................................................... 81

SPIS TREŚCI

O.P. Parenago, G.N. Kuzmina, V.D. Terekhin, K.Yu. Basharina:

Przeciwtarciowe i przeciwzużyciowe właściwości nanocząstek siarczków molibdenu syntezowanych z użyciem azotu zawierającego ciecze jonowe ...................................................... 7

A.V. Rădulescu, I. Radulescu, C. Cristescu: Eksperymentalne badania

zachowań reologicznych smaru olejowego H46 ........................ 15 R.G. Ripeanu, I. Tudor, I. Zidaru, Adrian C. Drumeanu: Wpływ

środka smarowego i płytek na tribologiczne charakterystyki trzypłytkowego łożyska stożkowego .......................................... 25

Z. Rymuza: Zaawansowane techniki badań nanotribologicznych .......... 33 Yu.P. Sharkeev, V.A. Kukareko, E.V. Legostaeva, A.V. Byeli:

Nanoatrukturalne materiały kompozytowe na bazie stopu tytanu i cyrkonu ze zmodyfikowaną warstwą wierzchnią dla zastosowań medycznych i inżynierskich .................................... 45

S. Strzelecki, S. M. Ghoneam: Wpływ zmian luzu łożyskowego na

maksymalną temperaturę filmu smarowego 3-powierzchniowego cylindrycznego łożyska ślizgowego ......... 52

K. Wierzcholski, A. Miszczak: Wpływ adhezji na rozkład prędkości

oleju i siły tarcia w szczelinie stożkowego łożyska ślizgowego.................................................................................. 61

K. Wierzcholski, A. Miszczak: Wpływ adhezji na rozkład prędkości

oleju i siły tarcia w szczelinie walcowego łożyska ślizgowego .................................................................................................... 71

N.V. Zaitseva, S. М. Zakharov, О. А. Shmatko, I. L. Oborskyi:

Wpływ parametrów procesu wibracyjnego na zmienność składu chemicznego i właściwości elektroiskrowe stali ............. 81


1 (161) 2010

O.P. PARENAGO*, G.N. KUZMINA* V.D. TEREKHIN*, K.YU. BASHARINA*

Antifriction and antiwear properties of molybdenum sulfides nanosized particles synthesized using nitrogen containing ionic liquids

K e y w o r d s

Molybdenum compounds, thermolysis, molybdenum sulfides, nanoparticles, solubility, lubricants, antifrictional and antiwear properties.

S u m m a r y

We have developed the synthesis pathways of molybdenum trisulfide nanoparticles that are soluble in hydrocarbon media and demonstrate their activity as antifrictional and antiwear additives to lubricants. Bis(tetraalkylammonium)tetrathiomolybdates as precursors of molybdenum trisulfide nanoparticles are synthesised by the interaction of ammonium thiomolybdate with tetraalkylammonium halides, including alkyl groups of the various types. The properties of synthesised molybdenum compounds were determined by UV- and IR-spectroscopy and by thermogravimetric analysis. The molybdenum trisulfide nanoparticles were formed by thermolysis of these compounds, and their sizes and size distribution were determined by small angle X-ray spectroscopy. The antifrictional and antiwear activity of molybdenum compounds and MoS3 nanoparticles were evaluated using various types of tribometers.

* A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky

prospect, 29, Moscow, Russia, [email protected]

O.P. Parenago, G.N. Kuzmina, V.D. Terekhin, K.YU. Basharina

8

1. Introduction

Sulfur containing molybdenum compounds are well known as the most active friction modifiers. Molybdenum disulfide is applied for many years as an additive to lubricants. Natural MoS2 (α-MoS2) has hexagonal structure (a trigonal prism) of the layered type and is similar to graphite in form. The layers of such a compound have the low shear resistance. They promote "smoothing" of the micro-surface, thus reducing the specific pressure and friction coefficient [1].

This compound, however, is not soluble in most solvents, including lubricants. This is why its application is limited to the grease additives [2], and sulfur containing molybdenum compounds are usually applied for the fabrication of synthetic lubricants [3]. The molybdenum dialkyldithiophosphates (MoDTP) and dialkyldithiocarbamates (MoDTC) are most widely used in practice [4,5]. These molybdenum compounds reveal fine antifrictional and antiwear properties, but their synthesis is extremely difficult, poorly reproducible and requires the use of carefully cleaned solvents that are free of oxygen. Additionally, hazardous and toxic substances (amines, phosphorus pentasulfide and carbon disulfide) are used as initial reagents.

As it has been shown by many authors (see, for example [3-6]), the МоDTP and МоDTC decompose to molybdenum disulfide in the course of tribological contact of rubbing metal surfaces, i.e. in the conditions of increased loadings and heated molybdenum.

It is known that molybdenum is capable of forming some sulfides, including molybdenum trisulfide, MoS3, depending on the valence condition. This compound is thermally unstable; and, while being heated, it easily forms the more stable molybdenum disulfide with the elimination of elemental sulfur [7, 8].

In this connection, it was interesting to synthesise the nanoparticles of molybdenum trisulfide, to provide their solubility and stability in a hydrocarbon media for their subsequent test as tribological active additives to lubricants. To synthesise nanoparticles, the technique of thermal decompositions of molybdenum sulfur containing compounds in a hot amphiphilic matrix was used.

2. Experimental

The synthesis of MoS3 nanoparticles was performed in a glass reactor through the interaction of a DMFA solution of ammonium thiomolybdate with tetraalkylammonium halides at 25оС for one hour [9]. An additional increase in temperature up to 150оС and mixing for two hours causes the precipitation of molybdenum trisulfide. The solvent was removed in a vacuum after cooling of

Antifriction and antiwear properties of molybdenum sulfides nanosized particles… 9

the mixture, and MoS3 particles were extracted with i-octane. The quantitative elemental analysis shows [Mo] : [S] ratio in the range of 1:2.5 - 1:3.1.

Special compound-modifiers were proposed to provide the solubility of molybdenum trisulfide nanoparticles in hydrocarbon media, in particular, in lubricants that are can coordinate with nanoparticles and keep them in the solution. The amines and ammonium derivatives, dithiophosphorus acids, derivatives of dialkyldithiocarbamic acids and, also, the alkylated succinamide have been used as such modifiers. Our solution of nanoparticles was stable at least for 1 year in the presence of the last modifier. Modifiers are typically entered into a reaction mixture through the interaction of ammonium thiomolybdate with tetraalkylammonium halides when their mass relation to the molybdenum is ~ 4.

MoS3 nanoparticles were characterised by UV- and IR-spectroscopy and thermo-gravimetry methods. The thermolysis mechanism of bis(tetraalkylammonium)tetrathiomolybdates was studied by IR Fourier spectroscopy in a special cell. The sizes of MoS3 nanoparticles were determined by small angle X-ray scattering technique (SAXS). Tribological properties were studied by different types of tribometers. The metal surface subjected to the friction process was studied by atomic force microscopy (AFM).

3. Results and discussion

It has been shown that at the first stage, the following exchange reaction took place:

2R4N+X - + (NH4)2MoS4 → [(R4)N]2MoS4 + 2NH4X, (1)

Where X = Сl or Br. Our studies of reaction products of the thermal decomposition of

molybdenum containing compounds show that, besides molybdenum sulfides, by-products like sulfur- and nitrogen containing compounds are formed:

(R4N)2MoS4 → 2R3N + R2S + MoS3 (2)

(R4N)2MoS4 → 2R3N + R2S2 + MoS2 (3)

The target of further examination was to study the effect of the alkyl group nature in nitrogen containing compounds on the mechanism of MoS3 nanoparticles formation and on their properties, and in particular, on their sizes. For this purpose the following compounds have been used as initial reagents for interaction with ammonium thiomolybdate: [(С4Н9)4N]Br, [(СН3)2(С18Н37)2N]Br, [С16Н33(СН3)3N]Br, [CH3(C8-C10)3N]Cl and [CH3(C8H17)3N]Cl. The thiomolybdate derivatives as precursors of nano-MoS3 formation have been received, isolated, and studied. It


10

should be stressed that the following compounds have been synthesised and described for the first time: [(CH3)3C16H33N]

+2[MoS4]

-2, [CH3(C8H17)3N]+

2[MoS4]-2,

[CH3(C8-С10)3N]+2[MoS4]-2 and [(CH3)2(C18Н37)2N]+2[MoS4]-2. The synthesised molybdenum complexes have been characterised by optical spectroscopic techniques. In the UV-spectral region of studied compounds, all bands are similar to the ones described in the literature for such compounds [10]. They have three pronounced maxima at 475, 324 and 245 nm, corresponding to σ (Mo-Mo) →π * (Mo-S) and σ (Mo-Mo) →σ * (Mo-S) electronic transitions in tetrahedral MoS24 - groups [11].

The results obtained from IR spectra of molybdenum compounds are given in Table 1.

Table 1. IR absorption bands of bis(tetraalkylammonium)tetrathiomolybdares

N, n/n Mo-compound ν(Mo=S), cm-1 Ν(C-N), cm-1 Ν(C-C), cm-1

I [(C4H9)4N]2MoS4 467 940 1479,1377, 734 II [C16H33(CH3)3N]2MoS4 470 930 1467, 1378, 720 III [CH3(C8H17)3N]2MoS4 469 942 1463, 1377, 719 IV [CH3(C8-С10)N]2MoS4 473 942 1466, 1379, 722 V [(CH3)2(C18Н37)2N]2MoS4 466 942 1467,1375, 721

There are characteristic bonds which correspond to functional groups Mo =

= S and CN in molecules besides of the bands belonging to С-С-bonds. Thermal characteristics of synthesized bis(tetraalkylammonium)tetrathio-

molybdates were studied gravimetrically. The following thermal stability series of bis(tetraalkylammonium)tetrathiomolybdates has been received from the data:

[C16H33(CH3)3N]2MoS4 > [(C4H9)4N]2MoS4 > [CH3(C8H17)3N]2MoS4 > [CH3(C8-С10)N]2MoS4 > [(CH3)2 (C18Н37)2N]2MoS4. The regularities of [(R4)N]2MoS4 thermolysis, leading to nano-MoS3

formation was studied using the special cell and a IR-Fourier spectrometer. The dynamics of Mo-derivatives decomposition is given in Fig. 1 at different temperatures. The most intensive band (at 469 cm-1 has weak, but quite a pronounced “shoulder” is found at 447 cm-1. These bands are related to valence vibrations of Mo=S-bond, and the most intensive one belongs to MoS4

2 - anion. The “shoulder” at 447 sm-1 belongs, most likely, to Mo=S-bonds as well, but in more complicated thiomolybdate clusters.

As indicated in Fig. 1, the intensity of bands related to Mo=S-bond decreases with temperature quite significantly. Further the bands at 500-530 cm-1 appear and start to grow in intensity with temperature 140оС. According to [12], these bands can be associated with the S-S-bond in the bridge cluster structures of thiomolybdates. The intensity of these bands decreases with temperature at 140оС. Above 180оС, the bands characterising Mo=S and S-S-bonds disappear in the spectrum of the compound. Such temperature behaviour of the S-S-bond is the indirect confirmation of the intermediate formation of MoS3 that turns to molybdenum disulfide by further heating.


Fig. 1. IR-spectra of [(C4H9)4N]2MoS4 ih the absorbance region of Mo = S-bonds The thermolysis of Mo-compounds results in the isolation of nano-MoS3.

The element analysis shows S:Mo ratios in the rage from 2.5:1 to 3.1:1. To reveal the nanoparticles sizes and size distribution, the SAXS-technique

was used (Fig. 2, Table 2). Our studies show (see Fig. 2) that the particles obtained by the thermolysis

of butyl derivative have a quite narrow unimodal distribution with average diameter ~ 50 nm.

Fig. 2. Size distribution of nano-MoS3, obtained by thermolysis of [(C4H9)4N]2MoS4


12

Table 2. The sizes of nano-MoS3, obtained by thermolysis of [R1R2R3R4N]2MoS4

Nanoparticles diameter, nm Mo-compounds Size distribution

1 signal 2 signal

[(C4H9)4N]2MoS4 (I) Unimodal 50 -

[C16H33(CH3)3N]2MoS4 (II) Bimodal 17 64

[CH3(C8H17)3N]2MoS4 (III) Unimodal 70 -

[CH3(C8-С10)N]2MoS4 (IV) Tetramodal 30 65

[(CH3)2(C18Н37)2N]2MoS4 (V) Bimodal 15 56

As indicated in Table 2, the unimodal distribution of sizes takes place for

the molybdenum compounds (with rather short alkyl groups - I and III) with the nanoparticle diameters being quite large. The nanoparticles formed from molybdenum compounds with rather long alkyl radicals (II and V) are characterised by the bimodal distribution of the sizes (with 16 nm and 60 nm average size). For nanoparticles obtained based on Mo-compounds, which include a composition (С8-С10) of alkyl fragments, the tetramodal distribution was shown. In this case, one narrow peak corresponds to the size of 30 nm. Three groups of particles with a rather low concentration of 65, 100 and 175 nm diameter were found here (the last two groups are not presented in Tab. 2).

The antifrictional and antiwear properties have been studied for both bis(tetraalkylammonium)tetrathiomolybdates and nano-MoS3 (obtained from these compounds). The antiwear activity of [R1R2R3R4N]2MoS4 was tested by a four-ball tribometer. In this case, solutions of Mo-compounds in dioctylphtalate were used as a model of synthetic lubricant, and the samples were loaded with 200 N for 60 min.

As indicated in Fig. 3, concerning the dependence between wear spot diameter and [Mo] concentration in solution, all the Mo-compounds reveal antiwear activity in the examined range of molybdenum concentration but do not affect the anti-scuffing property, i.e. the critical loading of seizure Pk in the presence of Mo-compounds does not change. The highest efficiency is revealed for [(C4H9)4N]2MoS4. This can be caused by the highest rate of its decom-position in the course of friction and the formation of triboactive molybdenum sulfides. For the same reason, the least antiwear activity is found for the complex having two bulk octadecyl groups (compound V).


The ability of Mo-compounds to reduce the friction coefficient was examined for two [Mo] complexes at 200-500 ppm concentrations. The tests performed on tribometer (with "disk-block" friction couple) show that the compounds under study demonstrate antifrictional properties and reduced friction coefficient with respect to the pure lubricant.

Fig. 3. Dependence between wear spot diameter and [Mo] concentration in dioctylphtalate solution; the curve number corresponds to the number of Mo-compound in the Tables 1 and 2

To determine a metal surface profile, the AFM technique was used. In the

case of pure lubricant, the average arithmetic deviation of a surface profile in the area of wear (measured in a direction perpendicular to the wear direction) was 100±20 nm at 16 µm base length. When the Mo-compound with lubricant are used, the profile diagram has 5±1.5 nm deviation of a surface profile in the area of wear (at the same 16 µm base length). The AFM analysis shows that the presence of the Mo-additive results in considerable (more, than 10 times) smoothing (reduction of roughness) of the metal surface, which confirms indirectly the formation of the MoS2 layer, making strong impact on the modification of surface profile.

The dependence between the friction coefficient and loading presented in Fig. 4 for solutions of Mo-compounds based on nano-MoS3 in Vaseline oil clearly demonstrate their antifrictional properties. According to the data, the greatest effect is reached in the case of nano-MoS3, obtained from the tetrabutyl derivative of molybdenum.


14

Fig. 4. The dependence between the friction coefficient and the loading value for nanoparticles, obtained from different Mo- compounds

Therefore, in this work, a new approach to nano-MoS3 synthesis is realised,

and a means of obtaining their stable dispersions in lubricants is found. The characteristics of MoS3 nanoparticles and their activity as antifriction and antiwear additives to lubricants are determined.

References

[1] Chermette H., Rogemond F., El Beqqali O. et al.//Surf. Sci. 2001 V. 472 P. 97-110. [2] Rastogi R.B., Yadav M.//Tribol. Int. 2003 V. 36. No.7. P. 511-516. [3] Mitchell P.S//Wear. 1984 V. 100. P. 281-300. [4] Yamamoto Y., Gondo S., et al.//Wear. 1986 V. 112. No.1. P. 79-87. [5] Zajmovskaja T.A., Lozovoj J.A., Kuzmina G. N, Parenago O. P. // Petroleum Chemistry.

1995. V. 35. № 4. P. 364-369. [6] Graham J., Spikes H., Korcek S.//Tribol. Trans. 2001 V. 44. No.4. P. 626-636. [7] Killefer D.H., Linz A.//Molybdenum Compound (Their Chemistry and Technology). 1952.

Interscience Publishers. N.-Y.-London. 407 p. [8] Afanasiev P.//C. R.Chimie. 2008.V. 11. P.159-182. [9] Patent N 2302452. Russian Federations 2007 [10] Poisot M., Bensch W., Fuentes S., Alonso G.//Thermochimica Acta. 2006 V. 444. P. 35. [11] Wu L., Zhang Y., et al.//J. of Molecular Structure (Theochem). 1999 V. 460. P.27. [12] Weber Th., Muijsers J.C. et al., J. Phys. Chem. 1995 V. 99. P. 9194.

Manuscript received by Editorial Board, April 23rd, 2010

Experimental study on the rheological behaviour of H46 lubricant oil 15


1 (160) 2010

RĂDULESCU ALEXANDRU VALENTIN*, RĂDULESCU IRINA**, CRISTESCU CORNELIU***

Experimental study on the rheological behaviour of H46 lubricant oil

K e y w o r d s

Rheology, lubricant, thermal, experiment.

S u m m a r y

This paper aims to characterise the rheological behaviour of hydraulic lubricants in relation to the testing temperature. The oil has been tested on a Brookfield rheometer with a cone and plate geometry. In order to determine the rheological model, the variation between shear stress versus shear rate was measured. The thermal properties of the oil were measured by studying the dependence between viscosity and temperature. Finally, a few laws for the variation of the viscosity with temperature have been proposed.

1. Introduction

Rheology refers to a set of standard techniques that are used to experimentally determine rheological properties of materials (fluid or solid). The idea underpinning rheology is to realise flows, where the stress and/or

* POLITEHNICA University of Bucharest, ROMANIA, e-mail: [email protected] ** S. C. ICTCM S.A. Bucharest, ROMANIA, e-mail: [email protected] *** INOE 2000 - IHP Bucharest, ROMANIA, e-mail: [email protected]

AV. Rădulescu, I. Rădulescu, C. Cristescu

16

strain fields are known in advance, which make it possible to deduce rheological properties from measurements of flow properties, [1], [2]. A rheometer is usually an experimental stand, which can exert a torque/force on a material and accurately measures its response with time (or conversely, it can impose a strain and measures the resulting torque). All the measurements can be done normally in a field of temperature between 15°C and 75°C, [3], [4].

The main purpose of the study is the experimental determination of rheological properties of H46 lubricant, mainly used in hydraulic power. The properties considered are as follows: • The rheological model of lubricant in a new and used state (with a wear

degree); and, • The variation of viscosity versus temperature, which is made for imposed

various velocity gradients. The method of regression analysis was used to determine the laws of

parameter variation for mentioned properties, and the confidence intervals are also established.

The physical and chemical properties of H46 oil are presented in Table 1, [6].

Table 1. The physical and chemical properties of H46 oil, [6]

Characteristic parameter H46

Density at 15°C 900 kg/m3

Viscosity at 40°C 41.4 – 50.6 cSt Viscosity at 100°C 24.2 – 31.4 cSt Viscosity Index 92 Viscosity CCS at 30°C 5500 cP Pour point - 25° C Flash point COC 200° C TBN 9.4 mg KOH/g Volatile factions 10 % Viscosity HTHS (150°C) 3.3 cP Colour (ASTM) L 3.5

2. Experimental stand and methodology

The experimental test stand was a Brookfield cone-plate viscometer, (Figure 1) [7]. The liquid is placed between a cone and a disc; one is moving and the other is stationary. For large opening angles of the cone (Figure 2), the rate of strain is constant across the gap, which is the advantage of this device. The viscometer is suitable for digital data acquisition, and it offers the possibility for one to determine the variation of viscosity by the temperature.


Fig.1. Brookfield cone-plate viscometer Fig. 2. Cone geometries

To determine the lubricant rheological model in a new and used state (with a wear degree), an “imposed velocity gradient” test, with the variation limits 100 ... 2000 s-1 and 22°C reference temperature was used. The tests were carried out with a load up to 2000 s-1 and unloading up to 0 s-1, in order to highlight the effects of lubricant thixotropy.

There were tested the two fluids and there were calculated the lubricant rheological parameters, by using the rheometer software, beyond the non-Newtonian fluids model, for the power law:

n

dy

dum

=τ (1)

Where m - consistency index (which is equivalent to the Newtonian fluid

viscosity) n - flow index (equal to 1 if the fluid is Newtonian).

To determine the viscosity variation law versus temperature for the

analysed lubricant, there were made only tests for new lubricant, for four imposed velocity gradients: 500, 1000, 1500 and 2000 s-1 and for a temperature range of 15 ... 75°C. The laws of variation assumed are as follows: • The Jarchov and Theissen model:

tt

Be +

−⋅= 95

50

50ηη (2)

Where η – viscosity; η50 – viscosity at 50°C; B – non-dimensional parameter; t – temperature.


18

• The Cameron model:

tb

Ke += 95η (3) Where η – viscosity; K – viscosity parameter; b – temperature parameter; t –

temperature. • The Reynolds model:

( )50

50−= tmeηη (4)

Where η – viscosity; η50 – viscosity at 50°C; m – temperature parameter; t – temperature.

The parameter values of the variation laws were determined using the

regression analysis method, by using MathCAD software, [5].

3. Results

Lubricant rheograms for new and used states are presented in Figures 3 and 4. The results for lubricant rheological parameters in new and used states are

directly obtained by using the rheometer software (Capcalc V3.0), (see the Figures 5 and 6). Results are centralised in Table 2.

500 1000 1500 2000Shear Rate (1/sec)

50

100

150

She

ar S

tres

s (N

/m²)

0.070

0.080

0.090

0.100

0.110

0.120

Vis

cosi

ty (

Pa·

s)

Brookfield Engineering Labs

File Data

H46 nou1000 Shear Stress (N/m²)

H46 nou1000 Viscosity (Pa·s)

Fig. 3. Lubricant rheogram for fresh state


500 1000 1500 2000Shear Rate (1/sec)

50

100

150S

hear

Str

ess

(N/m

²)

0.080

0.090

0.100

0.110

0.120

Vis

cosi

ty (

Pa·

s)


File Data

H46 uzat1000Shear Stress (N/m²)

H46 uzat1000Viscosity (Pa·s)

Fig. 4. Lubricant rheogram for used state

Table 2. The lubricant rheological parameters in fresh and used state

Lubricant type Consistency index

(m), Pa·sn Flow index (n) Correlation coefficient

H46 fresh lubricant 0.144 0.939 93%

H46 used lubricant 0.180 0.902 93.5%

100 1000Shear Rate (1/sec)

10.0

100

She

ar S

tres

s (N

/m²)


Analysis Plot: Power Law File: H46 nou1000

Consistency Index = 0.144 Pa·s Flow Index = 0.939 Confidence of Fit = 93 %

Raw Data

Fitted Curve

Fig. 5. Numerical regression for the results of new lubricant


20

100 1000Shear Rate (1/sec)

10.0

100S

hear

Str

ess

(N/m

²)

Brookfield Engineering LabsAnalysis Plot: Power Law File: H46 uzat1000

Consistency Index = 0.18 Pa·s Flow Index = 0.902 Confidence of Fit = 93.5 %

Raw Data

Fitted Curve

Fig. 6. Numerical regression for the results of used lubricant

For the new state lubricant, the results concerning the viscosity variation versus the temperature are obtained for the imposed velocity gradients: 500, 1000, 1500 and 2000 s-1 and for a 15…75°C temperature range (Figures 7, 8, 9 and 10).

Fig. 7. Viscosity versus temperature variation for new lubricant, at the 500 s-1 velocity gradient


22

4. Discussion

To determine the characteristic parameters for the viscosity variation related to temperature, we used MathCAD software. The results are presented in Table 3. Table 3. The characteristic parameters of the viscosity variation law versus temperature for H46 oil

Jarchov and Theissen model Parameter Velocity gradient, s-1 η50, Pa⋅s B Correlation coefficient

500 0.02454 5.90199 0.99812 1000 0.02167 6.20840 0.99616 1500 0.01737 6.86477 0.99425 2000 0.01404 7.31500 0.99106

Cameron model Parameter Velocity gradient, s-1 K, Pa⋅s b,

0C Correlation coefficient

500 6.7093⋅10-5 855.76735 0.99616 1000 4.3654⋅10-5 900.08298 0.99616 1500 5.99809⋅10-5 846.50065 0.99616 2000 0.98789⋅10-5 1052.7700 0.99616

Reynolds model Parameter Velocity gradient, s-1 η50, Pa⋅s m,

0C-1 Correlation coefficient

500 0.02250 -0.05466 0.99849 1000 0.01954 -0.05805 0.99947 1500 0.01466 -0.06609 0.99893 2000 0.01117 -0.07208 0.99715

The comparison between the results of the numerical regression and

experimental results is presented in Figures 11, 12, 13 and 14.

Fig. 11. The comparison between the results of the numerical regression over the experimental

results, for 500 s-1


Fig. 12. The comparison between the results of the numerical regression over the experimental

results, for 1000 s-1

Fig. 13. The comparison between the results of the numerical regression over the experimental results, for 1500 s-1


24

Fig. 14. The comparison between the results of the numerical regression over the experimental results, for 2000 s-1

5. Conclusions

1. The lubricant rheological parameters have been determined, and the difference between new lubricant characteristics and used ones was obtained.

2. Experimental tests showed lubricant thixotropy at high velocity gradients, which is present also for the new lubricant and for the used one.

3. Both for the new or used state, the lubricant behaviour is almost Newtonian, and the viscosity is presented in Table 2.

4. All three analysed models used for viscosity variation versus temperature are available. Their characteristic parameters are presented in Table 3.

5. Increasing the velocity gradient obtained a sliding of the lubricant wall for temperatures higher than 60°C.

References

[1] Hutter, K. and Jöhnk, K.: Continuum Methods of Physical Modeling, Springer, Berlin, 2004. [2] Barnes, H.A., Hutton, J.F. and Walters, K.: An introduction to rheology, Elsevier,

Amsterdam, 1997. [3] Coleman, B.D., Markowitz, H. and Noll, W.: Viscometric flows of non-Newtonian fluids,

Springer-Verlag, Berlin, 1966. [4] Truesdell, C.: The meaning of viscometry in fluid dynamics, Annual Review of Fluid

Mechanics, 6 (1974), pp. 111–147. [5] Crocker, D.C.: How to use regression analysis in quality control, American Society for Quality

Control, Vol. IX, 1983. [6] *** Oil catalog SC ICERP SA Ploiesti, http://www.icerp.ro/fise/Lubricerp/Uleiuri [7] *** Catalog CAP 2000+ viscometer, www.brookfieldengineering.com/

Manuscript received by Editorial Board, March 3rd, 2010

The lubricant and implants influence above tribological behaviour at three cone bits bearings 25


1 (161) 2010

RAZVAN -G. RIPEANU*, IOAN TUDOR*, ION ZIDARU**, ADRIAN -C. DRUMEANU*

The lubricant and implants influence above tribological behaviour at three cone bits bearings

K e y w o r d s

Three cone bits bearings, friction coefficient, copper implants.

S u m m a r y

Sliding bearings at three cone bits are lubricated in heavy conditions. To improve tribological behaviour, samples of bearing materials were made with implants with antifriction materials having different rapports between the implant and free base material in the presence of different greases. Tests made on a CSM microtribometer and on an Amsler A135 were to establish the proper implant rapport, measuring friction coefficient, and wear. The behaviour of the greases containing P.T.F.E was also established. In a second phase of the tests was designed and realised a device for testing three cone bits bearings at real axial loads. A SPIDER 8 device and inductive traducers were used to establish the friction coefficients and the temperature on the friction surface, depending on implants’ dimensions and grease lubricant type.

* Affiliated at: Petroleum-Gas University of Ploiesti, Blvd. Bucharest, No.39, Ploiesti, Romania;

e-mail: [email protected]; [email protected]; e-mail: [email protected] ** Affiliated at: S.C. UPETROM – 1 Mai Group S.A., St.1 Decembrie, No.1, Ploiesti, Romania;

e-mail: [email protected]

R.G. Ripeanu, I. Tudor, I. Zidaru, A.C. Drumeanu

26

1. Introduction

A drill bit is a complex device working at great deep supporting loads, especially at fast drilling, greater than 300 kN and speed over 500 r.p.m., [1]. At three cone drill bearing active surfaces, we have abrasive, erosive, corrosive, adhesive and impact wear at variable loads. These heavy working conditions are rarely meet in surface industry, so construction, materials and technology used in drill bit manufacturing have to solve many problems.

This paper presents the results and the solutions to increase the durability of three cone bits sliding bearings. It is very important that the lubricant to not be contaminated with drilling fluid. Because the properties of rubber used for sealing are maintained at 80°C, the temperature in sliding bearings must not exceed this temperature.

The loading capacity of sliding bearings depends on the surface cover capacity of the copper implants used [1, 2]. This work is to establish the proper implant rapport and the behaviour of new lubricant grease about wear, friction coefficient, and temperature at three cone bits sliding bearings.

2. Experiments

On universal testing machine type Amsler A135, we established the speed and grease influence, and measured the friction coefficient, wear, and temperature. The behaviour of the greases containing P.T.F.E. was also established. On the CSM microtribometer, the friction coefficient related to the implant rapport was also established. In a second phase of the tests, was designed and realised a device for testing three cone bits bearings at real axial loads. With SPIDER 8 device and inductive traducers, we establish the friction coefficients and the temperature at the friction surface in relation to implant dimensions and the grease lubricant type.

2.1. Experiments on Amsler machine

Tests were made on cylindrical surface couple, [1, 2] consisting of the following: – Shoe material 20MoCrNi06 (0.17...0.23%C, 0.60...0.90%Mn,

0.20...0.35%Si, 0.35...0.65%Cr, 0.35...0.76%Ni, 0.20...0.30%Mo, S and P max.0.025%, Cu max. 0.3%) with implants of copper;

– Cylinder surface layer of METCO Stellite 20. On shoe surface implants of copper [1] were made. Temperature was

measured with a thermocouple type J and a multimeter type APPA 306. The thermocouple was inserted in the shoe sample close to the friction surface.

The testing conditions were as follows: – normal load 1250 N at wear tests;


– cylinder rotation speed 200 r.p.m; – lubricant: – classical grease; – new grease with P.T.F.E.

In Figure 1 are presented the results for friction coefficients.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 25 50 75 100 125 150 175 200Normal load, daN

Fri

ctio

n co

effic

ient

, f

classical grease, v=0,314m/s grease with PTFE, v=0.314m/s

classical grease, v=0.418m/s grease with PTFE, v=0.418m/s

classical grease, v=0.628m/s grease with PTFE, v=0.628m/s

Fig. 1. Friction coefficient vs. normal load

The cylinder samples diameters were 30 mm, 40 mm and 60 mm. The capability

of shoe copper implants to cover the cylinder surface is maximum at the minimum tested diameter. As shown in Fig.1, the friction coefficients are smaller at 0.314 m/s (diameter 30 mm) and in the presence of new grease with classical P.T.F.E.

Figure 2 represents the gravimetric wear curves at sliding speed of 0.314 m/s.

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60Time, min.

Wea

r, m

g

cylinder- classical grease shoe- classical grease

cylinder- grease with PTFE shoe- grease with PTFE

Fig. 2. Wear curves at sliding speed of 0.314 m/s


28

Similar wear curves were obtained at 0.418 m/s and 0.628 m/s. The wear values are smaller at minimum sliding speed (friction length is smaller) and in the presence o new lubricant grease.

Table 1 presents the temperature tests results [1].

Table 1. Temperature results on Amsler shoe sample

Sliding speed, va, m/s Lubricant Time, min. Temperature, 0C

Classical grease 82

0.314 Grease with PTFE 76

Classical grease 84

0.418 Grease with PTFE 81

Classical grease 88

0.628 Grease with PTFE

60

83

From the values presented in Tab. 1, it could be observed that temperatures were smaller in the zpresence of new grease with P.T.F.E. powder. Because the lubrication was realised manual, in an open system, the obtained temperature values were rather over the recommended values.

2.1. Experiments on CSM microtribometer machine

Tests were made on plane surface couple, [3, 4] consisted of the following: – Disk sample: carburized, layer METCO Stellite, 12 copper implants, 15

copper implants; – Plane sample (static partner): surface 15.21 mm2 with layer of METCO

Stellite 20; – Dry friction, air temperature 20oC, relative humidity RH=48.7%; – Sliding speed 0.2199 m/s; – Normal load 4N; and, – Friction length 100m.

Figure 2 indicates the friction coefficients vs. friction length results for disk with 12 copper implants disposed at an 11 mm diameter, which means a sub-unitary rapport between implants length and the rest of material length.

Changing the rapport between the length of implant and the length of rest of material at a rapport of 1, obtained at 15 implants, tend to smaller values for the friction coefficient as presented in Figure 4.


Fig. 3. Friction coefficients vs. friction length for disk with 12 copper implants

0

0.05

0.1

0.15

0.2

0.25

0 20 40 60 80 100

Friction length, m

Fri

ctio

n c

oef

ficie

nt

Disk with 12 implants

Disk carburized

Disk with 15 implants

Disk with Stellite layer

Fig. 4. Friction coefficients vs. friction length


30

2.3. Experiments on a device for testing three cone bits bearings at real axial loads

A plan axial sliding bearing is designed to support the entire axial load, which is the action on cone during the drilling. Figure 5 represents the construction of the axial sliding bearing, and Figure 6 represents the relative position of the copper implants depending on the zone covered with stellite [1, 2].

Fig. 5. Construction of axial sliding bearing Fig. 6. Relative position of implants

Taking into account the following:

n – represents the implant number; l – distance between two implants; and,

7D

lK = the covering coefficient.

Table 2 presents the dimensions for axial sliding bearing drill bit type S– 8 ⅜ GJ [1].

Table 2. Dimensions of axial sliding bearing

Type and drill dimension

d6 mm

d7 mm

b mm

d0 mm

D6 mm

D7 mm

n implants

l mm

K -

s mm

S – 8 ⅜ GJ

50 35 7.5 42.5 45 5 6 18.55 3.71 0

To evaluate the friction coefficient and temperature, a special device [1, 2]

was designed. Axial load and friction torques are measured using two strain gauges and a strain traducer, type SPIDER 8, and Catman Easy soft program. Temperature was measured with a J type thermocouple. Figure 7 shows the samples dimensions [1, 2].

Samples with 6, 8 and 12 copper implants at an axial load of 5000 N and rotation speed of 120 r.p.m. in the presence of classical grease and new grease with P.T.F.E. were tested.


a b

Fig. 7. Samples dimensions: a – fixed sample button type with stellite layer; b – mobile sample type con with implants

Figure 8 represents the friction coefficient results at couple button with a

stellite layer and a cone carburized and with 8 copper implants in the presence of the classical drill bit grease

00.10.20.30.40.50.60.70.8

0 50 100 150 200

Time, sec.

Fri

ctio

n c

oef

fici

ent,

f

Fig. 8. Friction coefficient at couple materials with 8 copper implants and classical drill bit grease

Similar results were obtained in different conditions and are presented in

Table 3.


32

Table 3. Friction coefficients and temperature results

Materials couple

Lubricant Friction

Coefficient Temperature

oC Materials

couple Lubricant

Friction coefficient

Tempera-ture oC

Classical grease

1.30 80 Classical grease

0.75 66 Carburized stratum/ Stellite layer

Grease with P.T.F.E.

0.87 70

Carburized stratum with 8 implants/ Stellite layer


0.3 – 0.6 62

Classical grease

0.90 67 Classical grease

0.55 – 0.80 74 Carburized stratum with 6 implants/ Stellite layer Grease with

P.T.F.E. 0.82 – 0.87

63

Carburized stratum with 12 implants/ Stellite layer


0.75 70

3. Conclusions

Main conclusions resulted after the tests are as follows: • Using P.T.F.E. powder in the actual drill grease to obtain a new grease, the

friction coefficient and temperature at the friction surface were reduced; and, in the presence of drill grease with P.T.F.E., the friction coefficients decrease with a tendency to stabilise at a smaller value than at the starting friction.

• A temperature rise is with a smaller gradient in the presence of drill grease with P.T.F.E.

• Copper implants on the frontal carburized surface of axial sliding bearing diminish friction coefficient and temperature and at drill bit 8 3/8 GJ for the three types of implants number, the best solution was with 8 copper implants, when the smallest values for the friction coefficients and temperature were obtained.

References

[1] Ripeanu R.G. et al.: Research above rising durability at three cone drill bits (in Romanian), Research contract no. 45, Petroleum-Gas University of Ploiesti, 2008.

[2] Zidaru I., Ripeanu R.G., Tudor I., Drumeanu A.C., Research regarding the improvements of tribological behavior in three cone bits bearings, FME Transactions, Vol. 37, No. 2, pp. 99-102, 2009.

[3] Balaceanu M., Braic V., Kiss A., Zoita C.N., Vladescu A., Braic M., Tudor I., Popescu A., Ripeanu R.G., Logofatu, C. and Negrila, C.C., Characteristics of arc plasma deposited TiAlZrCN coatings, Surface and Coatings Technology, Vol. 202, No. 16, pp. 3981-3987, 2008.

[4] Ripeanu R.G., Drumeanu A.C., Luca M., Ripeanu L., Establishment of the influence of soybean oil on wear behavior of cutting tools durability, J. of the Balkan Tribological Association, Vol. 14, No. 4, pp. 490-499, 2008.

Manuscript received by Editorial Board, March 1st, 2010

Advanced techniques for nanotribological studies 33


1 (161) 2010

ZYGMUNT RYMUZA*

Advanced techniques for nanotribological studies

K e y w o r d s

Nanotribology, nanotribometry, atomic force microscope (AFM), nanoindentation.

S ł o w a k l u c z o w e

Nanotribologia, nanotribometria, mikroskop sił atomowych (AFM), nanoindentacja.

S u m m a r y

The advanced techniques used in nanotribological studies are discussed. Various techniques such as Atomic Force Microscopy (AFM), Surface Force Apparatus (SFA), Nanoindentation technique, etc. are described and their suitability to study friction on a nano- scale are evaluated. Some examples of the use of these instruments for nanotribological studies are given.

1. Introduction

Nanotribology is very fascinating area of tribological science and technology. It can reveal the behaviour of nanotribological systems down to nearly the atomic level. The results are useful in understanding the behaviour of * Warsaw University of Technology (Politechnika Warszawska), Institute of Micromechanics and

Photonics (Instytut Mikromechaniki i Fotoniki), ul. Św. A. Boboli 8, 02-525 Warszawa, tel. 0-22 2348540, e-mail: [email protected]

Z. Rymuza

34

macrotribological systems as well. The nanotribological studies have both a fundamental character and the results are applied in the Micro Electro Mechanical Systems (MEMS), Hard Disk Drives (HDD) technologies as well as in nanotechnologies (e.g., in nanoimprint lithography).

Nanotribology started practically after the construction of first atomic force microscopes (AFM) in the 1980’s [1-11]. The first experiments were carried out in the IBM laboratory in San Jose (USA) by M. Mate [2, 3]. He can be treated as the pioneer of Nanotribology followed by R. Kaneko in Japan and B. Bhushan in the USA [6, 8, 9]. Presently, dynamic progress can be observed, because many physicists and chemists have joined the research community of tribologists, the demands for the results of the nanotribological studies have been greatly increased.

2. Advanced techniques for nanotribological studies

The techniques used for nano- and macrotribological studies are completely different. The typical tribometers and rubbing pairs are not applicable in nanotribological research. The tribological parameters such as friction (friction coefficient) and wear rate are usually accompanied by the results of the adhesive (stiction) studies (pull-off force, stiction force, wetablility, surface energy) as well as by nanomechanical properties (nanohardness, elasticity modules on nano-scale – usually the properties of ultra-thin (with thickness below 1 µm) films are needed to understand the tribological data. In addition, such specific tests as nano-scratch is used but not for e.g. the estimation of the coating`s adhesion to the substrate but rather for rapid recognition of the tribological properties in particular of very thin films (e.g. 3-5 nm thick films applied as overcoat on magnetic layer in computer hard disks).

The fundamental instrument used in nanotribological studies is the atomic force microscope (AFM) [1, 6]. It is the device that enables the studies of friction and wear as well as estimate many other characteristics of the rubbing components on the atomic level. The principle of the instrument is shown in Fig. 1.

The rubbing pair is composed of the tip (usually with a very small radius = 5-100 nm) fixed to the cantilever (flat spring), which is in contact the sample material. The area of contact can be very small (e.g. with radius 0.5 nm). The applied load are usually on the level of nN-µN and sliding speeds in the range of 0.02-100 µm/s. The study of friction to obtain the friction map is a scan performed in the area below 50 µm x 50 µm. The additional surface topography (2D and 3D images), scratch test with the visualisation of its results as well as force-distance curve (to estimate pull-off force and to perform nano-indentation) can be done with the use of the same cantilever.


Fig. 1. Schematic of atomic force microscope (AFM)

Rys. 1. Schemat budowy mikroskopu sił atomowych (AFM)

It is evident that, with the use of the cantilever with very sharp tip, the

friction map will be presenting the lateral force that results from the adhesive interactions (material properties) and the mechanical interactions that result from the roughness. However, in nanotribological studies, the surfaces of the tested samples are very smooth so the effect of the roughness can be very small.

The results of the studies with the use of a AFM enable one to compare the tribological, adhesive, and mechanical properties of often studied ultra-thin films. The results of the measurements are very useful for the evaluation of the quality of materials useful in the construction of, e.g. MEMS devices. This is particularly important to the surface topography as confronted with the friction map.

The nano-scratch and nano-wear tests enable one to compare the wear resistance of tested materials (in particular ultra-thin films) devoted to the construction of the dubbing components of micro/nanosystems. Such test forces to use special cantilevers (usually very stiff) with very hard (diamond) tip. At scratching, the maximum depth of the scratch scar is evaluated at the defined load, scratch speed, and mode of scratching (single scratch, multiplied scratch). The shear force is very often also measured. The nano-wear test is rather complex, time consuming, and expensive. At the first moment, the surface of the sample is scanned at a low load to obtain its image. Then, at a smaller scan area (e.g. 2 x 2 µm), the nano-machining line by line is realised to form a nano-crater in the tested material (film). By the comparison of two scans, one obtained before the nano-machining and the second one after the wearing process, the wear depth, and the shape of the nano-crater can be visualised. Different shapes

Z. Rymuza

36

of the crater can be easily obtained and visualised (e.g. a nano-well with “nano-stairs”).

The second device, which is very useful to study friction on nano-scale, is the surface force apparatus (SFA) invented by J. Israelachvili and D. Tabor [7]. It was invented to study the molecular force interactions (Van der Waals forces) of very flat (mica) surfaces, being in intimate contact but having relatively small curvatures (Fig. 2). Nowadays, the SFA is also applied to study interfacial lateral (friction) forces at the shearing ultra-thin (molecular) of lubricant both in static and dynamic conditions. The interferometry is usually applied to identify the film thickness.

Fig. 2. Schematic of components (surfaces) used in studies of surface interactions and friction (shearing) with use of the surface force apparatus. Left-surfaces coated with a thin layer of liquid

(lubricant) are used in centre–surface interactions, and the right model is used for theoretical studies of surface interactions

Rys. 2. Szkic elementów stosowanych w badaniach z użyciem aparatu do pomiaru sił powierzchniowych. Po lewej – badane powierzchnie pokryte cienką warstwą cieczy (smaru),

w środku – oddziaływania powierzchni, po prawej – model do analizy teoretycznej oddziaływań powierzchni

In the studies of friction on the atomic level, sometimes it is useful to apply

the quartz crystal microbalance [2, 6, 9]. The pioneer of these studies was J. Krim (USA). In this case, the oscillating quartz crystal is used as the heart of the instrument.

The Quartz Crystal Microbalance (QCM) is used to measure friction dissipation for adsorbed layers sliding over surfaces. The QCM consists of a thin single crystal of quartz with metal electrodes deposited on its top and bottom surfaces. A thin film of atoms or molecules adsorbed causes the resonance frequency of the crystal to shift to a lower frequency. The film slides over the surface and dissipates its kinetic energy via friction, which broadens the resonance. The QCM measurements of interfacial friction are limited to sliding systems with very low friction, such as adsorbed rare gases or small physisorbed molecules. Noble metals are used for electrodes to have lower bonding energies. The schematic of the QCM is presented in Fig. 3.


Fig. 3. Schematic of quartz crystal microbalance Rys. 3. Schemat mikrowagi zbudowanej na drgającym krysztale kwarcu

For the practical studies of tribological properties of micro/nano-

tribosystems, special microtribometers are constructed [12-16]. They are used to identify the friction/wear between rubbing components, e.g. in hard disk drives, MEMS/NEMS devices, etc. In the last case, special test structures integrated with actuators and sensors to applied loads and move the components as well as to measure friction are fabricated with the use of microelectronic silicon technology [17]. After use, the microtribometer can be discarded.

In nanotribology, nanomechanical and adhesive studies are also very important. Very effective is nano-indentation with the use of special nano-indenters [18]. This technique enables one to estimate nanohardness and elasticity modulus of very thin films. The adhesive studies are realised with the use of AFM via the realisation of force-distance curves (FDC). Such test enables in particular the estimation of the pull-off force needed to remove the tip (probe) from the contact with a sample. At well-known geometries of the contacting surface (tip–sample), this FDC procedure enables one to estimate interfacial surface energy. A very effective additional test is the wetablility test, which, using very small droplets, enable one to estimate surface energy on a very small area. The droplets can have very small diameters: 30-50 nm.

3. Applications of advanced techniques in nanotribology

The AFM found the most effective application in nanotribological studies. The family of Scanning Probe Microscopes (SPM) based on the sharp tip is very wide now. The application of only AFM creates very exciting possibilities that are schematically show in Fig. 4.

Z. Rymuza

38

Scanning probe microscopy

Contact Mode

Imaging

Static forcespectroscopy

Topography

Friction forcemapping

Intermittent ContactMode (Tapping)

Dynamic forcespectroscopy

Imaging

Topography Phase contrast

“Severe” dynamiccontact mode

NanoindentationNanoscratchingLocal wearing

Fig. 4. Modes of operation of the scanning probe microscopy/atomic force microscope used for nanotribological/nanomechanical studies

Rys. 4. Mody pracy mikroskopu skaningowego z sondą/mikroskopu sił atomowych przy badaniach nanotribologicznych/nanomechanicznych

Contact mode is most common in the study of the surface topography and

friction. Tapping mode is necessary to study the surface topography of polymeric (elastic) materials (Fig. 5).

Fig. 5. Examples of surface topography of two polymeric resist materials used in nano-imprint lithography. AFM images obtained in tapping mode

Rys. 5. Przykłady topografii powierzchni dwóch polimerowych rezystów stosowanych w technice nanoimprintingu otrzymane przy pracy AFM w modzie tapping (oscylująca sonda)

In nanotribological studies with the use of a AFM, the friction loop (friction

force vs. displacement at forward and backward movement of the sliding element) can be easy created (Fig. 6), which can be used to estimate static and friction coefficient of friction as well as preliminary displacement of the surface layers of the contacting material before transition to sliding can be identified.


Fig. 6. Friction loop obtained with the use of AFM Rys. 6. Pętla tarcia uzyskana przy użyciu AFM

The scratch test is relatively simple and cheap, and it can give some

interesting results about the wear resistance of the tested material (ultra-thin films) (Fig.7). The depth of scratch scar can be used as criterion for preliminary estimation of wear resistance.

1000 uN

Fig. 7. Scratch scar and its cross-section obtained with a diamond tip on carbon coating

Rys. 7. Obraz śladu zarysowania igłą diamentową powłoki węglowej

Z. Rymuza

40

The nano-wear test can be easily carried out with the use of a AFM and stiff cantilever with a diamond tip. The wear crater is visualised with the use of the same tip (Fig. 8).

Fig. 8. Example of nano-wear scar and its cross-section Rys. 8. Przykład krateru nanozużycia i jego przekrój

The nano-indentation enables one to easily identify nanohardness and the

elasticity modulus of very thin films. The continuous load-distance characteristics (Fig. 9a) with the Pharr and Oliver formula is used for [16]. Also, a nice AFM image of very small indention can be obtained by scanning (Fig. 9 b).


Fig. 9. Nanoindentation: a – Load vs. indentation depth during loading and unloading, b – AFM image of indent

Rys. 9. Nanoindentacja (nanowgłębnikowanie): a – siła vs. głębokość odcisku przy obciążaniu i odciążaniu, b – odcisk uzyskany z AFM

Summary

Nanotribology has become a very import and interesting area of advanced interdisciplinary studies. The results of nanotribological studies are very important for understanding the fundamentals of tribological phenomena, and they play a very important role in the progress of nanotechnology, in particular, in the area of MEMS/NEMS, magnetic recording, and nano-imprint lithography technologies.

Z. Rymuza

42

The advanced techniques used in the studies of tribological problems on a nano-scale have enabled rapid grow of this area of science and technology. In particular, the inventions of the scanning probe microscopy techniques and the AFM have enabled much progress in the nanotribological studies.

References

[1] Bhushan B., Fuchs H., Hosaka (eds): Applied Scanning Probe Methods. Springer Verlag. Berlin 2004.

[2] Mate C.M., McClelland G.M., Erlandson R., Chiang S.: Atomic-scale friction of a tungsten on a graphite surface. Physical Review Letters 59 (1987) 1942-1945.

[3] Mate C.M.: Tribology on the Small Scale: A Bottom Up Approach to Friction, Lubrication, and Wear. Oxford University Press. Oxford 2007.

[4] Bhushan B. (ed): Handbook of Micro/Nanotribology.2nd edition. CRC Press. Boca Raton 1999.

[5] Meyer E., Hug H.J., Bennewitz R.: Scanning Probe Microscopy: The Lab on a Tip. Springer Verlag. Berlin 2004.

[6] Bhushan B. (ed): Nanotribology and Nanomechanics: An Introduction. Springer Verlag. Berlin 2005.

[7] Israelachvili J.N.: Intermolecular and Surface Forces. Academic Press, 2nd edition. London 1991.

[8] Bhushan B. (ed): Tribology Issues and Opportunities in MEMS. Kluwer Academic Publishers. Dordrecht 1998.

[9] Bhushan B. (ed). Handbook of Nanotechnology. Springer Verlag. Berlin 2004. [10] Scherge M., Gorb S.: Biological Micro- and Nanotechnology: Nature`s Solutions. Springer

Verlag. Berlin 2001. [11] Hirano M.: Study on Atomistic Friction. PhD Dissertation. The University of Tokyo. Tokyo

1998. [12] Dubois Ph., Von Gunten,S. Enzler A., Lippuner U., Dommann,A. De Rooij,

N.Reciprocating silicon microtribometer, Proceedings of SPIE - The International Society for Optical Engineering, v. 4980, p 163-174, 2003.

[13] Williams J.A., Le H.R., Tribology and MEMS, Journal of Physics D: Applied Physics, v 39, n 12, p R201-R214, May 21, 2006.

[14] Van Spengen W.M., Frenken K.W., The Leiden MEMS tribometer: Real time dynamic friction loop measurements with an on-chip tribometer,Tribology Letters, v 28, n 2, p 149-156, November 2007.

[15] Ku, I.S.A, Reddyhoff, T.; Choo, J.H.; Holmes A.S.; Spikes, H.A., A novel tribometer for the measurement of friction in MEMS, Tribology International, v 43, n 5-6, p 1087-1090, May 2010/June 2010.

[16] Desai A.V., Haque M.A., A novel MEMS nano-tribometer for dynamic testing in-situ in sem and tem: Proceedings of the ASME/STLE International Joint Tribology Conference, IJTC 2004, n PART B, p 1617-1624, 2004, Proceedings of the ASME/STLE International Joint Tribology Conference, IJTC 2004.

[17] Madou M., Fundamentals of Microfabrication, 2nd ed., CRC Press, Boca Raton 2002. [18] Fischer-Cripps A., Nanoindentation, 2nd ed., Springer Verlag, Berlin 2004.

Manuscript received by Editorial Board, May 8th, 2010


Zaawansowane techniki badań nanotribologicznych

S t r e s z c z e n i e

W artykule przedstawiono zaawansowane techniki badań nanotribologicznych. Opisano różne techniki, takie jak mikroskopia sił atomowych (AFM), aparat do pomiaru sił powierzchnio-wych (SFA), techniki nanoindentacji (nanowgłębnikowania) i oceniono ich przydatność do bada-nia tarcia w nanoskali. Podano też przykłady wykorzystania niektórych technik do badań nano-tribologicznych.

YU.P. Sharkeev, V.A. Kukareko, E.V. Legostaeva, A.V. Byeli

44

Nanostructured composite materials on the base of titanium and zirconium… 45


1 (161) 2010

YU.P. SHARKEEV*, V.A. KUKAREKO** E.V. LEGOSTAEVA*, A.V. BYELI***

Nanostructured composite materials on the base of titanium and zirconium with modified surface layers for medicine and engineering

K e y w o r d s

Titanium, zirconium, modified surface layers.

S u m m a r y

This paper presents the results of the investigations of mechanical and tribological properties of ultrafine-grained and nanostructured titanium and zirconium under microplasma and ion beam treatments. It indicates that the nitrogen ion beam treatment of titanium and zirconium at low temperatures essentially increases the wear resistance by 35–50 times and reduces the friction coefficient by 40%. The biocomposite (nanostructured titanium - calcium phosphate coating) demonstrates a high friction coefficient (0.4–1.0) in tribological interaction with an ultrahigh molecular polyethylene imitated of subcutaneous tissue and bone tissue that allows to eliminate the microdisplacements of an implant against bone tissue under friction and to increase its fixation. A considerable improvement of tribological characteristics of the nanostructured titanium and zirconium with the modified surface layers give the advantages for these materials in medicine and engineering.

* Institute of Strengths Physics and Material Science of RAS, Russia, 634021, Tomsk,

pr. Academicheskii 2/4, Е-mail – [email protected] ** Joined Institute of Mechanical Engineering of NASB, Belarus, 220072, Minsk,

pr. Academicheskii 12. *** Physical-Technical Institute of NASB, Belarus, 220141, Minsk, Kuprevicha st., 10.


46

1. Introduction

The surface modifications of materials by ion beam and microplasma (also known as plasma electrolytic oxidation (PEO) and micro-arc oxidation (MAO)) methods are advanced perspectives for the enhancement of tribological and anticorrosive characteristics. Moreover, the use of severe plastic deformation methods ensures the formation of the bulk ultrafine-grained and nanostructured states that allows the improvement of the mechanical and tribological properties. Thus, the bulk structure and surface modification methods open new perspectives to the development of novel composite materials with modified surface layers for medical and engineering applications.

Over the years, the scientific groups from Institute of Strength Physics and Materials Science SB RAS, Physical&Technical Institute of NASB, Joined Institute of Mechanical Engineering of NASB take part in the development and investigation of ultrafine-grained and nanostructured titanium and zirconium with modified surface layers.

The paper presents the results of the systematic investigations of structure and phase states, mechanical and tribological properties of ultrafine-grained and nanostructured titanium and zirconium under microplasma and ion beam treatments.

2. Experimental details

Technically pure titanium (VT1-0 and VT1-00 in Russia or Grade 1 and Grade 2 abroad) and iodide zirconium were chosen to prepare the investigation subjects. Two methods of severe plastic deformation were used to obtain titanium and zirconium billets in ultra-fine-grained and nanostructure states. These methods are equal-channel angular pressing [1] and uniaxial abc-pressing in a press-mould with the rolling in groove rollers [2]. Then the samples were cut from the billets to modify the surface layer with ion-beam and microplasma methods.

Ion beam processing was performed on the vacuum installation equipped with a gas ion source of self-contained electron drift [3]. The nitrogen ion energy was equal to 3 keV and the ion current density was equal to 2 mA/cm2. The titanium sample temperature during ion-beam nitration varied in the range of 620 – 820 K.

In order to form calcium-phosphate coatings on the titanium surface, the technological technique Micro-Arc-3.0 was developed [4]. The aqueous solution of phosphoric acid with hydroxyapatite and calcium carbonate powders was used as the electrolyte. Tribological tests were carried out by using an automated tribometer [5]. The speed of titanium specimen movement was kept near 0.1 m/s. The tribological testing was carried out with the initial pressure of 1 MPa.


3. Experimental results

3.1. Ion-beam modification

The research results show that a fragmented structure is formed in titanium and zirconium during severe plastic deformation in the range of е = 0.8 – 1.44. This structure contains a high density of dislocation tangles (Fig. 1). The increase in deformation up to e = 2.1 leads to the formation of ultradispersed subgrains transformed from extended band fragments. The subsequent increase in deformation up to е = 2.49 leads to the formation of ultrafine-grained structure with the grain size of 0.2 – 0.3 µm [6]. The microhardness of deformed titanium increases by 55–60%, that of zirconium, by 90-100%.

The nitrogen ion-beam treatment of titanium and zirconium at the temperatures of 770–820 К results in the formation of a modified surface layer with the thickness of ≈5 µm containing nitrogen solid solution in hexagonal lattice α-Ti and α-Zr. Thus, the microhardness of the surface layer increases up to 3500–3700 МPа [7].

Fig. 1. TEM bright field images and corresponding selected area diffraction of titanium microstructure: a) the initial state; b) after severe plastic deformation of е = 1.44;

c) after severe plastic deformation, е = 2.1

Fig. 2a shows the dependence of mass wear on the friction path of the titanium in the initial state (Curve 1), after the equal-channel angular pressing (е = 2.1) (Curve 2) and after a nitrogen ion implantation at the temperature of 820 K (Curve 3). Fig. 2b shows the dependence of the friction coefficient of titanium specimens on the friction path. The mentioned data have shown that the curves of mass wear in the initial state and after the severe plastic deformation almost coincide. The intensity of titanium wear for these conditions of pre-treatment is 0.11–0.12 mg/m. The values of the friction coefficient of titanium samples in the initial state and after severe plastic deformation also keep the same level of 0.45–0.5.

0.3 µm 0.3 µm 1.5 µm

a b c


48

0 25 50 75 100 125 150 175 2000

5

10

15

20

25

3

2

1

Friction path, m

Mas

s w

ear,

mg

a

0 25 50 75 100 125 150 175 200

0,0

0,2

0,4

0,6b

3

21

Fric

tion

coe

ffic

ient

Friction path, m

Fig. 2. The dependencies of mass wear (a) and friction coefficient (b) on the friction path for titanium specimens subjected to treatments under various conditions (dry friction, Pа = 1 МPа).

1) the initial state; 2) the same + the severe plastic deformation, е = 2.1; 3) the same + the severe plastic deformation, е = 2,1,+ the nitrogen ion implantation at 820 К

Nitrogen ion implantation has a considerable influence on the tribological

properties of its surface layers. In particular, the titanium samples with a nitrogen ion-modified surface have a low wear rate of 0.003 mg/m at the initial stage of the tests. This stage is also characterised by the reduced friction coefficient level of 0.2–0.3. Subsequently, with the increase in the friction path and the wear of nitrogen-modified layer, the wear rate and the friction coefficient increase up to the value level corresponding to the initial unimplanted state of material.

Similar regularities of the dependence of the friction coefficient and mass wear on the friction path have been discovered during the testing of the iodide zirconium samples (Fig. 3). In particular, at the initial state, the wear rate is 0.23–0.25 mg/m, the friction coefficient is 0.4–0.5. A severe plastic deformation does not have an effect on a wear rate or a friction coefficient as in the case of titanium. The subsequent nitrogen ion-beam treatment leads to a significant decrease in a wear rate of 25–30 times down to ~0.009 mg/m and a friction coefficient down to 0.2–0.3.

0 25 50 75 100 125 150 175 200

0

10

20

30

40

50

321

Friction path, m

Mas

s w

era,

mg

a

0 25 50 75 100 125 150 175 200

0,0

0,2

0,4

0,6b

32

1

Fri

ctio

n co

effi

cien

t

Friction path, m

Fig. 3. The dependencies of mass wear (a) and friction coefficient (b) on the friction path of zirconium samples subjected to treatments under various conditions (dry friction, Pа = 1 МPа). 1) initial state; 2) the same + the severe plastic deformation, е = 2.1; 3) the same + the severe plastic deformation, е = 2.1 + the

nitrogen ion implantation at 820 К


Thus, the nitrogen ion-beam treatment of the VT1-00 titanium and zirconium increases considerably (25-30 times) the wear resistance of its surface layer and reduces the friction coefficient in tribocontact by 40%.

3.2. Microplasma electrolytic oxidation

In order to form bioactive surface layers enhancing the properties of metallic substrate (titanium in nanostractured state), depositing the calcium-phosphate coatings in the plasma of microarc discharges was suggested. The influence of electrophysical parameters of micro-plasma process (voltage and current values, pulse period and frequency, deposition time) and electrolyte compositions on physical, chemical, mechanical, and biological properties of coatings have been investigated. It was shown that the electrolyte based on an aqueous solution of orthophosphoric acid, hydroxyapatite, and calcium carbonate allows the production of porous calcium-phosphate coatings with high biocompatability. The coating structure is formed by layers, and it consists of thick oxide sublayer and upper porous layer, the basic components of which are spherolytes (Fig.4). Directly after depositing, the coating is in an X-ray amorphous state. Its interaction with a biological environment is characterised by a high speed of dissolution that indicates its bioactivity [8–9].

The optimal characteristics of the coatings connecting the high osseointegration and adhesion to substrate have been found. They are the following: Roughness is 2–6 µm, porosity is 20–35%, adhesion strength to the nanostructured titanium surface is up to 35 MPa, atomic Са/Р ratio is 0.7. The high adhesion strength of coatings was achieved by preliminary preparation of a titanium surface by corundum particles sandblasting and subsequent chemical etching in acid solutions of hydrochloric and sulphuric acids heated to boiling temperature.

TiK

TiK

PK

OK

CaK

СаK

8.0 10.09.0 7.06.05.04.03.0 2.0 1.0 0

0 10 20 30 40 50 60 70

Е, кэВ 2θ

Fig. 4. Microplasma calcium-phosphate coating produced in an electrolyte on the basis of orthophosphoric acid, hydroxyapatite and calcium carbonate: a) SEM image,

b) energy-dispersion X-ray spectrum, c) X-ray diffraction pattern

During the introduction of biocomposites in a living organism on the boundary “implant-bone,” there is a probability of microdisplacements that can


50

lead to the friction processes [10]. The behaviour of the biocomposite based on nanostructured titanium and calcium phosphate coating under the of dry friction condition and in biological fluid (0.9% sodium chloride solution) has been studied. The ultrahigh-molecular polyethylene samples were used as a counterface, since they are the most suitable to the strength properties of a bone (ultimate strength is 35-50 MPa). Moreover, the bone tissue samples were also used.

Tribological tests of the nanostructured titanium without a coating against ultrahigh-molecular polyethylene and bone tissue have shown a high wear resistance both under the dry friction condition and in 0.9% sodium chloride solution. Wear was not registered during the tests and a small friction coefficient of µ = 0.09 – 0.15 was observed (Fig. 5).

0 20 40 60 80 100

0,05

0,10

0,15

0,20

Fric

tion

coef

fici

ent

Friction path, m

1 2 3 4

Ti

Fig. 5. The dependence of the friction coefficient on the friction path for the nanostructured titanium samples produced by abc-pressing: 1) dry friction, counterface – ultrahigh-molecular polyethylene; 2) friction in 0.9% sodium chloride solution, counterface – ultrahigh-molecular polyethylene; 3) dry friction, counterface – bone tissue; 4) - friction in 0.9% sodium chloride

solution, counterface – bone tissue At the same time, the tribotesting of calcium-phosphate coatings against

ultrahigh-molecular polyethylene under the dry friction conditions have shown an invariably high friction coefficient within the range of 0.35–0.4 during all tests. However, the wear rate of the coating was small, and it is equal to 0.001 mg/m (Fig. 6). The longevity of the calcium-phosphate coatings in the 0.9% sodium chloride solution was less in comparison with the tribological tests without a lubricant. The wear rate was 0.002 mg/m, and the friction coefficient was up to 0.4-0.5. It is connected to the simultaneous dissolution of a coating in the solution. When using bone tissue as a counterface, the friction coefficient was up to 0.8-0.9 (Fig. 6).


0 20 40 60 80 100

1

2

3a

Mas

s w

ear,

mg

Friction path, m

1 2 3 4

Ca-P

0 20 40 60 80 100

0,25

0,50

0,75

1,00a

Fric

tion

coef

fici

ent

Friction path, m

1 2 3 4

Ca-P

Fig. 6. The dependence of a mass wear (a) and a friction coefficient (b) on the friction path for the nanostructured titanium samples with a calcium-phosphate coating: 1 – dry friction, counterface –

ultrahigh-molecular polyethylene; 2 – friction in physiologic solution, counterface – ultrahigh-molecular polyethylene; 3 - dry friction, counterface – ultrahigh-molecular polyethylene – bone

tissue; 4 - friction in 0.9% sodium chloride solution, counterface – bone tissue

Thus, a calcium phosphate coating stimulates an osseointegration, and, as

the tribological tests have shown, an infallible fixation of an implant due to a high friction coefficient.

Conclusion

The formation of ultrafine-grained and nanostructured states under severe plastic deformation of titanium and zirconium does not have a considerable influence on their wear resistance and friction coefficient under dry friction conditions. The nitrogen ion-beam treatment of the tested materials provides an increase in the wear resistance of their surface layers (25-30 times) as well as a decrease in the friction coefficient of the tribological interaction by ~40%. The microplasma electrolytic oxidation of the titanium in the orthophosphoric acid, hydroxyapatite and calcium carbonate solution allows the production of porous calcium-phosphate coatings with high physical-mechanical and tribological properties. A high friction coefficient of 0.4-1.0 during the frictional interaction with a ultrahigh-molecular polyethylene and a bone tissue allows one to avoid the displacements during the friction of the implant against a bone tissue, thus intensifying its fixation. A considerable increase in the tribological properties of nanostructured titanium and zirconium with the modified surface layers makes these materials quite promising in medicine as well as in engineering.

The work has been partially supported by the Russian Foundation of the Basic Researches, the project No. 08-03-00960а, Programs of Presidium of the Russian Academy of Science, (Fundamental sciences – for medicine), project No. 21.5 and Russian State contract, project No. 02.512.11.2285.


52

References

[1] Segal V.M, Reznikov V.I, Kopylov V.I, Pavlik D.A, Malyshev V.F., "Processes of structural forming of metals", Science &Technique, Minsk (1994) 223p.

[2] Bratchikov A.D, Sharkeev Yu.P, Kolobov Yu.R, Eroshenko A.Yu, Kalashnikov M.P., Method and device for deformation treatment of materials. RF Patent 2315117, (2008).

[3] Byeli A.V., Kukareko V.A., Lobodaeva O.V., Ion-beam treatment of metals, alloy and ceramic materials: Minsk, Physical and technical institution, 1998, 220 p.

[4] Shashkina G.A., Sharkeev Yu.P., Kolobov Yu.R., Karlov A.V., Calcium-phosphate coatings on titanium and titanium implants and method of its deposition. RF Patent 2291918, (2007)

[5] Karavaev M.G., Kukareko V.A. Automatized tribometer with forth and back motion / Proceedings of conference «Reliability of and machines and technical system», Minsk, 2001, P.37-39.

[6] Sharkeev Yu.P., Kukareko V.A., Eroshenko A.Yu., Kopylov V.L., Bratchikov A.D., Legostaeva E.V. , Kononov A.G., Tiu V.S, The regularities of the submicrocrystalline structures formation in titanium subjected to a severe plastic deformation under various conditions. Physical Mesomechanics. 2006. Volume 9. Special edition, P. 129-132.

[7] Byeli A.V., Kukareko V.A., Kononov A.G., Kopylov V.L., Sharkeev Yu.P., Legostaeva E.V. , and Eroshenko A.Yu., Microstructure and Wear Resistance of Titanium Subjected to Severe Plastic Deformation and Lon-Beam Nitriding. Proceedings of 9th International conference on modification of materials with particle beams and plasma plows, 21-26 September 2008. - Tomsk: Publishing house of the IAO SB RAS, 2008. - P.465-468.

[8] Sharkeev Yu.P., Kolobov Yu.R., Karlov A.V., Khlusov I.A., Legostaeva E.V., Shashkina G.A., Structure, mechanical and osteogenous properties of biocomposite material on the basis of submicrocrystalline titanium and microarc calcium-phosphate coating. Physical mesomechanics. 2005. Volume. 8. Special edition. P.83-86.

[9] Sharkeev Yu.P., Legostaeva E.V., Eroshenko A.Yu., Khlusov I.A., Kashin O.A., The Structure and Physical and Mechanical Properties of a Novel Biocomposite Material, Nanostructured Titanium–Calcium-Phosphate Coating». Composite Interfaces, 2009 (16) Р. 535-546.

[10] Legostaeva E.V., Sharkeev Yu.P., Kukareko V.A., Kononov A.G., Calcium-phosphate coatings on nanostructured titanium and their tribological behavior. 30th Annual Polish Tribological Conference „Advanced Tribology”, 21 - 24 September 2009, Radom, Poland – P. 61-68.

Manuscript received by Editorial Board, April 24th, 2010

The effect of clearance variation on the maximum temperature of the oil film… 53


1 (161) 2010

S. STRZELECKI*, S.M. GHONEAM**

The effect of clearance variation on the maximum temperature of the oil film of cylindrical 3-lobe journal bearing

K e y w o r d s

Theory of lubrication, multilobe journal bearings, maximum oil film temperature.

S ł o w a k l u c z o w e

Teoria smarowania, łożyska ślizgowe wielopowierzchniowe maksymalna temperatura filmu smarowego.

S u m m a r y

The variation of the journal bearing clearance has an effect on the bearing operation. It should be strictly controlled to avoid unexpected failures of the bearing. The changes in the clearance of the bearing cause the changes in its static and dynamic characteristics. An effect of the clearance on the oil-film temperature distribution and its maximum value is very important. The full characteristics of 3-lobe cylindrical journal bearings are not accessible in practice.

The paper presents the results of the theoretical investigation into an effect of bearing clearance on the oil film temperature distribution and its maximum value of 3-lobe cylindrical journal bearing. The oil film pressure and temperature distributions were obtained by numerical solution of the Reynolds, energy, and viscosity equations with the geometry equation.

* Department of Machine Design, Lodz University of Technology, Lodz, Poland. ** Mechanical Design & Production Engineering Department, Faculty of Engineering,

El-Monoufia University, Shebin-El-Kom, Egypt.

S. Strzelecki, S.M. Ghoneam

54

1. Introduction

The 3-lobe journal bearings [1-3] that are applied in the turbines and turbo-generators should assure long and reliable operation of this rotating machinery. As compare to the bearings with cylindrical bushes, they are characterised by good stability in the range of higher rotational speeds, assuring very good cooling conditions for the oil film. Any failure occurring during operation of these bearings can cause very high power loses. The part of static characteristics of the journal bearings consists of the oil film maximum temperature, which is very important factor in the process of reliable bearing design and others.

The 3-lobe bearings include the 3-lobe cylindrical bearing [1], classic bearing [1-2] or pericycloid bearing [3-5]. All these types of bearings have three lubricating pockets placed at 120°. The characteristic feature of classic 3-lobe bearing is the difference in radii between them. The single lobes of this bearing are designed as the arc of the circle with the centre points placed on the symmetry line of the single lobe. In the symmetric multilobe bearing, the circle inscribed in the bearing profile is tangent to the lobe exactly at the middle point of each lobe. In case of 3-lobe cylindrical bearing, the inscribing radius and the lobe radius are equal, and this bearing is designed as three parts bearing of cylindrical non-continuous profile [1].

The paper introduces theoretical investigation into the maximum oil film temperature of 3-lobe, cylindrical journal bearings. The Reynolds, energy, and viscosity equations were solved numerically on the assumption of incompressible lubricant, and on the laminar and adiabatic flow of oil in the lubricating gap of finite length bearing. The static equilibrium position of the journal was assumed in the calculations [1-5].

2. Oil film pressure and temperature distribution

scientific problems of sciences of machines...

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