ANALYSIS OF TRIBOLOGICAL CHARACTERISTICS OF THE …€¦ · F 2 0 rb P h S K Z (3) If F n is the normal force on the contact surface, then the friction coefficient μ is: 2 2 0 nn

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International Journal of Mechanical Engineering and Technology (IJMET)

Volume 9, Issue 1, January 2018, pp. 499–510, Article ID: IJMET_09_01_054

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=1

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

ANALYSIS OF TRIBOLOGICAL

CHARACTERISTICS OF THE RADIAL SLIDE

BEARINGS

Azem Kycyku, Naser Lajqi*, Shpetim Lajqi and Krenar Pllana

Faculty of Mechanical Engineering

University of Prishtina, 10000 Prishtina, Kosovo *Corresponding author

ABSTRACT

Machine elements, where tribological phenomena are more pronounced, are slide

bearings. Tribology is a science that analyzes friction, wear and lubricate and the

mutual action of the surfaces in contact when moving one part of the machine to the

other.

In this paper the characteristics of the radial slide bearings from the tribological

aspect will be analyzed. Since the friction is unavoidable on the sliding bearings, then

all the possible impacts will be analyzed in the paper, respectively the analytical

expressions and graphic representation of the friction coefficient will be presented,

which represents the component by which the best interpretation of this phenomenon.

Friction as a tribological characteristic of radial sliding bearings is an unavoidable

and undesirable phenomenon. Therefore, our tendency is that this coefficient has the

smallest value on these bearings.

In the paper, the impacts on friction coefficient are presented in detail, such as the

influence of viscosity of the lubricant, normal load, number of rotations, etc. Also in

the paper are explained the types of contact surfaces and the analytic expressions for

their calculation. Since the viscosity of the oil for lubricant bearings is of particular

importance, the effects on this viscosity are analyzed in the paper.

Keywords: Slide bearings, friction, wear, dynamic viscosity.

Cite this Article: Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana,

analysis of tribological characteristics of the radial Slide bearings, International

Journal of Mechanical Engineering and Technology 9(1), 2018. pp. 499–510.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=1

1. INTRODUCTION

Friction is part of the science of tribology, defined as a resistance force, which prevents the

relative movement between the surfaces in contact and which slide or rotate to one another.

Because of the frictional force on the contact surfaces of the machine elements, which is in

motion on one another, there appears energy - power loss. These losses of power result in

heating and wear of the parts that come in contact.

Analysis of tribological characteristics of the radial Slide bearings


There exist these types of friction:

dry friction occurs when direct contact is made between the surfaces of two bodies

which are in relative motion,

mixed friction, where contact occurs partly through direct contact and partly through

the lubricates, and

liquid friction, where the lubricates is present between contact surfaces, which are in

relative motion and based on the presence of the lubricates can be:

friction of semi-wet surfaces - "combination friction", and wetting wet surfaces -

"completely liquid friction" whereby the lubricates completely separates the contact

surface.

When solving practical problems, the frictional phenomenon is expressed through the

coefficient of friction and friction force. As a result of friction, the radial sliding bearings, as

well as other machine parts, result in the wear of the surfaces in contact.

The following types of wear are distinguished: adhesive, abrasive, fatigue, corrosion, etc.

In order to reduce friction, the lubricate is placed on the contact surface. The lubricate can

be in liquid (oils), consistency (grease), gaseous and solid.

2. FRICTION IN THE RADIAL SLIDE BEARING

In these bearings, during operation, the friction is slid into the contact surface between the

shaft sleeve and the bearing ring. The friction force on the contact surface between the sleeve

and the ring of the bearings will be:

Fµ = µ·Fn (1)

Where are:

µ - the friction coefficient depends on the materials of the parts in contact, the harshness of

the contact surfaces, the condition of the surfaces and other conditions.

Fn – the normal force of the contact surface.

The contact between the shaft and the ring of the bearing, in the case without load, is a

line contact. By the action of the load, respectively the radial (normal) force, due to elastic

deformations, this line is transformed into a quadrilateral.

Figure 1 Slide radiale bearing [1]

The friction force, according to [1], is calculated with the expression:

0tv

F Ah

(2)

Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana


When are:

A [mm2] - contact surface,

h [µm] - diameter area - thickness of the lubricates, and

ƞ0 [Pa·s] - viscosity of the lubricates at atmospheric pressure and constant temperature

vt [m/s]- peripheral speed of the shaft.

If the radius of the shaft sleeve is r, while the width of the bearing b, with the expression

of the peripheral speed of the shaft through the angular velocity ω and the radius r, then the

expression for the calculation of the friction force is:

2

02 r bF

h

(3)

If Fn is the normal force on the contact surface, then the friction coefficient μ is:

2

02

n n

F r b

F F h

(4)

The torques needed to overcome the strain on the lubricates layer is:

(5)

The friction moment on the bearings will be:

(6)

Where are:

r - shaft radius, b - bearing width, n - shaft speed, p - pressure in the lubricants layer.

In case of hydrodynamic lubricates, respectively when there is no direct contact between

the slive and the ring of the bearing, the moment of friction on the bearings will be equal to

the torque for overcoming the strain on the lubricates:

(7)

The lost power due to friction on the bearings becomes heat, is:

3 2

02v t

r bH F v T

h

(8)

Figure 2 Cross section of radial slide bearings [5]

Lubricant

Shaft

Bearing ring



Determination of the minimum diameter spacing between the shaft sleeve and the radial

sliding bearing ring depends on the diameter and number of shaft rotations.

Figure 3 Recommended Diametric Clearance for Oil Ring Lubrication [7]

From Figure 3, it can be seen that with the increase of the axis diameter, for the constant

number of rotations, the minimal diameter space increases. For the constant shaft diameter,

with the increase in the number of rotations, the minimum required space increases.

3. WEAR IN THE RADIAL SLIDE BEARING

As a consequence of the friction created on the contact surface between the sleve and the ring

of the bearing, the wear of the bearing ring occurs. Damage to the coating layer results in

damage to the bearing ring which has a negative impact on the work of the machine

Figure 4 Damage to radial ring slide bearings [6]

Damage to the radial slide bearings shown in Figure 4, occurred due to the direct contact

of the shaft surface and the bearing ring, caused by the elastic deformations of the axle under

load

The most common expense on radial slide bearings is: wear caused by adhesion, abrasion,

fatigue, corrosion, vibrations, etc.

The impact of these types of expenditures on the radial toggle bearings depends on several

factors, such as:

the rigidity of the bearing ring and the shaft ring

the roughness of the contact surfaces,

maintenance, including: type of lubricates, level of lubricates, type of lubricates, metal

particle hardness, splinters, etc., which are inserted between the contact surfaces of the

shaft sleeve and the bearing ring,

improper installation of the radial slide bearings and shaft,



overload, which is followed by eccentric deviations of the axis geometry of shaft and

geometry axis of the bearing ring, etc.

Figure 5 Schematic depiction of consumption due to: a) adhesion, b) abrasion,

c) surface fatigue and d) corrosion [38]

Adhesive wear is created as a result of microlights between the contact points of the

unobstructed contact of real contacting surfaces. In this way, the particles of the micro-edges

of one part attach to the rest (Figure 6).

Figure 6 Steps leading to adhesive wear [9]

According to Arckard, the volume of particles generated on this occasion calculates with

the expression:

(7)

Where are:

kad - adhesion coefficient (Arckard coefficient), F - normal force on contact surface,

S – path of movement, σt – strain on the material flow boundary.

Table 1 The adhesion coefficient values kad [2]

Type of material Hardness [daN/mm2]

Brass 60/40 6·10-4

95

Brass 70/30 2.5·10-5

5

Silver 6·10-6

320

Beryllium Bronze 3.7·10-5

210

Steel for seasoned tools 1.3·10-4

850

Steliti 5.5·10-5

690

Ferrous steel that does corroded 1.7·10-5

250

Tungsten carbide in soft steel 4·10-6

186

Bakelite 7.5·10-6

25

Abrasive wear is caused by the corrosion of the surface of the soft material from the

surface roughness of the strongest material (Figure 7).



The volume of particles generated during the abrasive blending, determines by expression:

(8)

Where are:

kab - the abrasive coefficient for different materials varies roughly according to the

diagram in Figure 8.

H- hardness of the softest material of the parts in contact.

Figure 7 The supposed volume of corrosion during abrasion Figure 8 abrasive coefficient

Wear from the surface fatigue of the material occurs when the load frequency values

exceed those frequencies that the material can withstand. Fatigue is caused by long-term

cyclical loads and working conditions such as: eccentric shaft, non-balancing, axial bending,

thermal loads, vibrations, etc. Radial slide bearings due to fatigue the wear of the bearings

ring (Figure 10 and Figure 11) usually occurs.

Figure 9 Edge Load Journal Shell with Babbitt Mechanical Fatigue [8]

Figure 10 Damaging the bearing ring by fatigue



4. GRAPHIC PRESENTATION OF TRIBOLOGICAL

CHARACTERISTICS

For engineers and technical personnel, the graphical representation of the relevant sizes is of

particular practical importance because it enables them to understand the size and

interpretation in order to draw conclusions of particular practical importance. Therefore, from

the expressions given in the paper, using the Mathcad application program, the graphical

representation of the main tribological characteristics of the radial slide bearings will be

presented.

4.1. Graphic representation of the coefficient of friction

Using the expression (4) given in the paper, for different values of normal force on the

bearings, the coefficient of friction is presented depending on the dynamic viscosity of the

lubricate.

10 16 22 28 34 40 46 52 58 64 70 76 82 88 94 1 102

0

3.5 104

7 104

1.05 103

1.4 103

1.75 103

2.1 103

2.45 103

2.8 103

3.15 103

3.5 103

3.85 103

4.2 103

4.55 103

4.9 103

5.25 103

5.6 103

5.95 103

6.3 103

6.65 103

7 103

1 ( )

2 ( )

3 ( )

4 ( )

5 ( )

6 ( )

Figure 11 The coefficient of friction depending on the viscosity of the lubricate for various loads; 1

for load 10 [kN], 2- for load 20 [kN], 3- for load 30 [kN], 4- for load 40 [kN], 5- for load 60 [kN], 6-

for load 80 [kN]

2

1

3

4

5

6



Figure 12 The friction coefficient depending on the load and the viscosity of the lubricants; 1- η = 10,

2- η = 20, 3- η = 30, 4- η = 40, 5- η=50, 6- η=60, 7- η= 70, 8- η = 80, 9- η = 90, 10- η = 100 [MPa·s]

1

2

3

4

5

6

7

8

9

1



0 2 4 6 8 10 12 14 16 18 20

1.15 104

2.3 104

3.45 10

4

4.6 104

5.75 104

6.9 10

4

8.05 104

9.2 10

4

1.035 103

1.15 103

1.265 10

3

1.38 103

1.495 10

3

1.61 103

1.725 103

1.84 10

3

1.955 103

2.07 10

3

2.185 103

2.3 103

2.415 10

3

2.53 103

2.645 10

3

2.76 103

2.875 103

2.99 10

3

3.105 103

3.22 10

3

3.335 103

3.45 103

3.565 10

3

3.68 103

3.795 10

3

3.91 103

4.025 103

4.14 10

3

4.255 103

4.37 10

3

4.485 103

4.6 103

1 n( )

2 n( )

3 n( )

4 n( )

5 n( )

6 n( )

7 n( )

8 n( )

9 n( )

10 n( )

n

1

2

3

4

5 6 7 8 9

10

[min-1]

Figure 13 Friction coefficient depending on the shaft speed and loads;

1- F= 20 [kN], 2- F= 40 [kN], 3- F= 60 [kN], 4- F= 80 [kN], 5- F= 100 [kN],

6- F=120 [kN], 7- F= 140 [kN], 8- F=160 [kN], 9- F=180 [kN], 10- F= 200 [kN]

4.2. Graphical presentation of overcoming constraints to disconnect lubricant

Using the expression (5) given in the work, for different values of the diameter of the shaft

sleeve, is presented the frictional torque depending on the dynamic viscosity of the lubricant.



10 16 22 28 34 40 46 52 58 64 70 76 82 88 94 1000

1.5

3

4.5

6

7.5

9

10.5

12

13.5

15

16.5

18

19.5

21

22.5

24

25.5

27

28.5

30

Tm.1 ( )

Tm.2 ( )

Tm.3 ( )

Tm.4 ( )

Tm.5 ( )

Tm.6 ( )

Figure 14 Torque for overcome the squeezing strainers of the lubricates depending on the viscosity of

the lubricates, for different diameters of the shaft sleeve; 1- ø 140 [mm], 2- ø 160 [mm], 3- ø 180

[mm], 4- ø 200 [mm], 5- ø 240 [mm], 6- ø 260 [mm]

4.3. Graphical presentation of power turned into heat due to friction

Using the expression (6) given in the work, for different values of the diameter of the shaft

sleeve, is shown the power, which is lost in the bearings due to friction and which is

converted to heat depending on the angular velocity of the shaft.

0 0.6 1.3 1.9 2.5 3.1 3.8 4.4 5 5.6 6.3 6.9 7.5 8.1 8.8 9.4 100

3.8

7.6

11.4

15.2

19

22.9

26.7

30.5

34.3

38.1

41.9

45.7

49.5

53.3

57.1

61

64.8

68.6

72.4

76.2

80

[s-1]

[W]

76.4

0

H.v1 ( )

H.v2 ( )

H.v3 ( )

H.v4 ( )

100

Figure 15 The lost power expressed in [W], for angular velocity and different diameter of the shaft

sleeve; 1- ø 140 [mm], 2- ø 160 [mm], 3- ø 200 [mm], 4- ø 220 [mm]

1

2

3

4



4.4. Change of oil viscosity depending on temperature and pressure

As the temperature rises, the viscosity of the lubricating oil of the bearings decreases, while

with increasing viscosity pressure increases.

Figure 16 Change of viscosity depending on temperature for different types of lubricates

Figure 17 Viscosity depending on the pressure for different types of lubricates; 1-η0 = 0.3, 2-η0 = 0.4,

3-η0 = 0.5, 4-η0 = 0.6, 5-η0 = 0.7, 6-η0 = 0.8, 7-η0 =0.9, MPa▪s.

1-η0 =0.3,

1-η0 =0.3,

1-η0 =0.3,

1

2

3

4

5

6

1

2

3

4

5

6



5. CONCLUSION

Based on the theoretical review and graphical presentation of the main tribological

characteristics of the radial sliding bearings, the following conclusions can be drawn:

friction and wear as a consequence of it are features of particular tribological

importance in these bearings,

for the constant value of the acting force on the bearings, the coefficient of friction

increases linearly with the increase of the dynamic viscosity of the oil (Figure11),

for the constant viscosity value (which cannot be assured during work), with the

increase of the normal force the coefficient of friction on the bearing decreases (Figure

12),

the frictional moment increases linearly with the increase of the viscosity of the

lubricate (Figure 14),

power losses in the sliding bearings, which become heat, increase progressively with

the increase of the angular velocity of the shaft (Figure 15),

for the constant number of shaft speed, the increase in axial diameter increases

frictional losses (Figure 3),

increasing the temperature affects the reduction of the viscosity of the lubricate

(Figure 16), while the increasing of the pressure affects the increasing of the viscosity

(Figure 17). In practice, these two parameters act simultaneously,

the volume of the material consumed by the adhesion increases linearly with the

increase of the normal force on the bearings, the larger diameter shafts produce more

weir material,

the volume of the consumed material by abrasive increases linearly with the increase

in normal force on the bearings.

Sizes established as certain information in the paper are a concrete example of the bearing

reducer excavator SRS-470, which is used in the Kosovo Energy Corporation, so graphical

results and conclusions presented in the paper are of practical importance.

REFERENCES

[1] S. Pehan & J. Fiser: Tribologija, Univerza v Mariboru, 2008.

[2] A. Rac: Osnovi tribologije, Univerzitet u Beogradu 1991.

[3] D. Zezelj: Istrazivanje nosivosti klizno – valjnih parova, Magistarski rad, Zagreb 2002.

[4] B. Opsiger: Proracun kruzno-cilindricnog lezaja s’hidrodinamickim podmazivanjem,

Rijeka 2001.

[5] K. Pllana: Analiza e ndikimit të ngarkesave në karakteristikat tribologjike te kushinetat

rrëshqitëse radiale, Punim i Masterit, Prishtinë 2017.

[6] KEK: Dokumentacioni teknik i Fabrikës së Proceseve dhe Pajimeve, Prishtinë.

[7] Pinkus, O.; Sternlicht, B.: Theory of Hydrodynamic Lubrication, Mcgraw-Hill, New

York- 1961

[8] http://www.machinerylubrication.com/Read/638/failure-analysis-bearings

[9] http://nptel.ac.in/courses/112102015/12

[10] http://www.machinerylubrication.com/Read/1375/wear-modes-lubricated

http://www.machinerylubrication.com/Read/638/failure-analysis-bearings

http://nptel.ac.in/courses/112102015/12

http://www.machinerylubrication.com/Read/1375/wear-modes-lubricated

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ANALYSIS OF TRIBOLOGICAL CHARACTERISTICS OF THE …€¦ · F 2 0 rb P h S K Z (3) If F n is the normal force on the contact surface, then the friction coefficient μ is: 2 2 0 nn