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2003 Course Tribology

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Total No. of Questions : 12] P1186 [Total No. of Pages : 5 [3664]-145 B.E. (Mechanical S/W) TRIBOLOGY (2003 Course) (402063) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) 2) 3) 4) 5) Answers to the two sections should be written in separate books. Neat diagrams must be drawn wherever necessary. Figures to the right indicate full marks. Use of logarithmic tables, slide rule and electronic pocket calculator is allowed. Assume suitable data, if necessary. SECTION - I Unit - I Q1) a) Explain tribological problems in industry. b) State desirable properties of lubricant. c) Explain API classification of lubricating oil. [8] [6] [2] OR Q2) a) Write a short note on Viscosity Index. [5] b) Compare Rolling contact bearings with Hydrodynamic bearings based on following points : [8] i) Starting Friction, ii) Load Carrying Capacity, iii) Speed and iv) Life. c) Determine the viscosity of the lubricant in centipoises having viscosity 160SUS and specific gravity 0.86. [3] Unit - II Q3) a) Using deformation theory prove that coefficient of friction due to deformation is directly proportional to semi-cone angle for conical asperity. [6] b) Explain Fretting and Percussion wear in detail. [6] c) Enumerate the factors affecting wear. [4] P.T.O. OR Q4) a) Assuming theory of ploughing of a soft surface by a hard conical shaped asperity, show that volume of wear is given by [8] Q= 2W cot 30 where, W- Load, - semi cone angle of the asperity and P0 yield pressure of the softer material. b) Write short note on following : i) Stick-Slip Friction. ii) Tomlinson s theory of molecular attraction. [8] Unit - III Q5) a) Show that the oil film thickness in case of hydrodynamic journal bearing [8] is given by h = c(1 + cos ) with usual notations. b) Explain Boyd-Raimondi s method for analysis of Hydrodynamic Journal Bearing. [10] OR Q6) a) Derive an expression for pressure p around a short journal bearing of L2 3U C sin y 2 with usual notations. [8] p= length L as RC3 (1 + cos 3 4 b) Following data is given for a 360 Hydrodynamic journal bearing : [10] Radial Load L/D ratio Bearing Length Journal Speed Radial Clearance Specific gravity of Lubricant Specific heat of lubricant = = = = = = = 10 kN 1 50 mm 1450 rpm 20 microns 0.86 2.09 kJ/kg C Calculate i) minimum oil film thickness. ii) the coefficient of friction. iii) power lost in friction. iv) viscosity of lubricant in cP and v) total flow rate of lubricant in l/min. [3664]-145 2 1 h o c S r f c Q Qs P rcn l Q P max s 0 0.1 0.2 0.4 0.6 0.8 0.9 0.97 1.0 l d 1.0 0.9 0.8 0.6 0.4 0.2 0.1 0.03 0 1.33 0.631 0.264 0.121 0.0446 0.0188 0.00474 0 (85) 79.5 74.02 63.10 50.58 36.24 26.45 15.47 0 26.4 12.8 5.79 3.22 1.70 1.05 0.514 0 3.37 3.59 3.99 4.33 4.62 4.74 4.82 0 0 0.150 0.280 0.497 0.680 0.842 0.919 0.973 1.0 0.540 0.529 0.484 0.415 0.313 0.247 0.152 Table 1 : Dimensionless Performance Parameters for full journal bearings with side flow. SECTION - II Unit - IV Q7) a) Derive the equation for flow rate of lubricating oil through rectangular slot with neat sketch. State its applications. [8] b) Explain the working of hydrostatic bearing with neat sketch. [8] OR Q8) a) Derive the equation for stiffness of hydrostatic step bearing. b) Following data is relates to a hydrostatic thrust bearing : Shaft diameter = 500 mm Recess diameter = 300 mm Shaft Speed = 720 rpm Viscosity of oil = 160 SUS Film thickness = 0.15 mm Specific gravity of oil = 0.86 Specific heat of oil = 1.76 kJ/kg C Thrust Load = 500 kN. [6] [10] Calculate :i) The supply pressure; ii) Flow requirement in l/ min; iii) Power loss in pumping; iv) Frictional power loss and v) Temperature rise assuming the total power loss in bearing is converted into the frictional heat. [3664]-145 3 Unit - V Q9) a) Derive equations for pressure distribution, load carrying capacity and time of approach for squeeze film lubrication between parallel rectangular plates. [10] b) Explain merits, demerits and applications of Gas bearings. [6] OR Q10) a) Derive an expression for average pressure, load carrying capacity and time of approach for squeeze film lubrication between parallel square plates. [8] b) A circular plate of 60 mm radius is approaching the base plane at a velocity of 150 mm/sec at the instant when the oil film thickness is 0.2 mm. If the absolute viscosity of the oil is 0.025 Pa-sec, calculate : i) The load carrying capacity of the oil film at the given instant; ii) The maximum pressure and iii) The average pressure. [6] c) What are essential operating conditions for gas lubricated bearings. [2] Unit - VI Q11) a) A fixed pad hydrodynamic thrust bearing of length L and width B has a fluid film shape given by relation : h = ho e ax Where ho = minimum film thickness and a = constant. Assuming side leakage as zero, derive an expression for pressure distribution. [10] b) The following data refers to the hydrodynamic tapered-pad bearing : Length of the pad Width of the pad Maximum oil film thickness Minimum oil film thickness Viscosity of the lubricant Sliding velocity = = = = = = 200 mm 850 mm 150 microns 75 microns 0.05 Pa-sec. 5 m/sec. Calculate : i) The load carrying capacity of bearing. ii) The pressure at a distance of 100 mm from leading edge. iii) Coefficient of friction. iv) Power lost in bearing. [3664]-145 4 [8] OR Q12) a) Write short notes on the following (any two) : i) Elastohydrodynamic lubrication. ii) Gaskets. iii) Dynamic Seals. iv) Sintered Metal Bearings [8] b) Explain different types of oil groove arrangements in journal bearing.[6] c) Enlist desirable properties of bearing materials. [3664]-145 5 [4]

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