ANALYSIS OF TRIBOLOGICAL CHARACTERISTICS OF THE RADIAL SLIDE BEARINGS

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 1, January 2018, pp , Article ID: IJMET_09_01_054 Available online at ISSN Print: and ISSN Online: 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, 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), pp 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 editor@iaeme.com

2 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: F µ = µ F n (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. F n 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: F v t 0 A h (2) editor@iaeme.com

3 Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana When are: A [mm 2 ] - contact surface, h [µm] - diameter area - thickness of the lubricates, and ƞ 0 [Pa s] - viscosity of the lubricates at atmospheric pressure and constant temperature v t [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: r b F (3) h If F n is the normal force on the contact surface, then the friction coefficient μ is: 2 F 2 0 r b F F h n n The torques needed to overcome the strain on the lubricates layer is: The friction moment on the bearings will be: 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: The lost power due to friction on the bearings becomes heat, is: r b Hv F vt T h (4) (5) (6) (7) (8) Lubricant Bearing ring Shaft Figure 2 Cross section of radial slide bearings [5] editor@iaeme.com

4 Analysis of tribological characteristics of the radial Slide bearings 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, editor@iaeme.com

5 Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana 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: Where are: k ad - adhesion coefficient (Arckard coefficient), F - normal force on contact surface, S path of movement, σ t strain on the material flow boundary. Table 1 The adhesion coefficient values k ad [2] Type of material Hardness [dan/mm2] Brass 60/ Brass 70/ Silver Beryllium Bronze Steel for seasoned tools Steliti Ferrous steel that does corroded Tungsten carbide in soft steel Bakelite Abrasive wear is caused by the corrosion of the surface of the soft material from the surface roughness of the strongest material (Figure 7). (7) editor@iaeme.com

6 Analysis of tribological characteristics of the radial Slide bearings The volume of particles generated during the abrasive blending, determines by expression: Where are: k ab - 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. (8) 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 editor@iaeme.com

7 Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana 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 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. 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] editor@iaeme.com

8 Analysis of tribological characteristics of the radial Slide bearings 1 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] editor@iaeme.com

9 Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana n [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 editor@iaeme.com

10 [W] Analysis of tribological characteristics of the radial Slide bearings T m.1 ( ) 22.5 T 21 m.2 ( ) 19.5 T m.3 ( ) T m.4 ( ) T m.5 ( ) T m.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 H 53.3.v1 ( ) 49.5 H.v2 ( ) H.v3 ( ) H.v4 ( ) 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] [s-1] editor@iaeme.com

11 Azem Kycyku, Naser Lajqi, Shpetim Lajqi and Krenar Pllana 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 5 3 Figure 17 Viscosity depending on the pressure for different types of lubricates; 1-η 0 = 0.3, 2-η 0 = 0.4, 3-η 0 = 0.5, 4-η 0 = 0.6, 5-η 0 = 0.7, 6-η 0 = 0.8, 7-η 0 =0.9, MPa s. 1-η 0 =0.3, 1-η 0 =0.3, 1-η 0 =0.3, editor@iaeme.com

12 Analysis of tribological characteristics of the radial Slide bearings 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, [2] A. Rac: Osnovi tribologije, Univerzitet u Beogradu [3] D. Zezelj: Istrazivanje nosivosti klizno valjnih parova, Magistarski rad, Zagreb [4] B. Opsiger: Proracun kruzno-cilindricnog lezaja s hidrodinamickim podmazivanjem, Rijeka [5] K. Pllana: Analiza e ndikimit të ngarkesave në karakteristikat tribologjike te kushinetat rrëshqitëse radiale, Punim i Masterit, Prishtinë [6] KEK: Dokumentacioni teknik i Fabrikës së Proceseve dhe Pajimeve, Prishtinë. [7] Pinkus, O.; Sternlicht, B.: Theory of Hydrodynamic Lubrication, Mcgraw-Hill, New York [8] [9] [10] editor@iaeme.com