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2003 Course Tribology (Elective II)

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Total No. of Questions : 12] [Total No. of Pages :4 [3864] - 155 B.E. (Mechanical S/W) TRIBOLOGY (2003 Course) ( Elective - II ) ( 402063 ) P1141 Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) 2) 3) 4) 5) 6) Answer 03 questions from section I and 03 questions from section II. 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, mollier charts, electronic pocket calculator and steam tables is allowed. Assume suitable data, if necessary. SECTION - I UNIT - I Q1) a) b) c) Q2) a) What are the different parameters which affect viscosity of oil? Discuss in brief . [6] State physical and chemical properties of Lubricants. [4] An Oil of viscosity of 50 cP and relative density of 0.9 is used for Lubrication convert the viscosity into Centistokes, SUS and Pascal second units. [6] OR Explain modes of Lubrication. [6] b) What is role of additives in lubrication? What are different additives used in lubricating oils? [4] c) Discuss in brief the role of tribology in industry. [6] UNIT - II Q3) a) b) c) Derive Archard s equation for volume of adhesive wear with assumptions made. State Laws of wear using above equation. [8] Explain Ferrography technique for measurement of wear. [4] Enumerate the factors affecting wear. [4] OR P.T.O. Q4) a) b) c) Q5) a) What is mean by:i) Contact area / contour area of contact. ii) Real area of contact. iii) Apparent area of contact. Explain the following theories of friction :i) Coulomb s classical theory. ii) Electrostatic theory of friction. iii) Tomlinson s theory of molecular attraction. [6] Explain stick - slip oscillations. [2] UNIT - III Derive the Renold s equation x b) Q6) a) h 3 p 3 p = 6 U h + h x y x x [8] [10] with usual notations. State the assumptions made in the equation. Show the axial and radial pressure distribution in the bearing. Explain Boyd-Raimondi s method for analysis of Hydrodynamic Journal Bearing. [8] OR Derive an expression for pressure p around a short journal bearing of length L as [10] 3U C sin L2 p= y 2 with usual notations. 3 RC 3 ( + cos ) 4 1 b) Following data is given for a 360o Journal bearing: [8] Journal diameter = 50 mm Bearing Length = 50 mm Radial load = 3.2 kN Journal Speed = 1490 rpm Radial Clearance = 0.05 mm Oil viscosity = 25 cP Assuming that the total heat generated in the bearing is carried away by the total oil flow in the bearing , calculate i) Minimum oil film thickness. ii) The coefficient of friction. iii) Flow requirement in litre/ min and. iv) Power lost in friction. [3864] - 155 -2- l d ho c 1 1.0 0.9 1.33 0.8 0.631 0.6 0.264 0.4 0.121 0.2 0.0446 0.1 0.0188 0.03 0.00474 0 0 0 0.1 0.2 0.4 0.6 0.8 0.9 0.97 1.0 S r f c (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 Q rcn l s 3.37 3.59 3.99 4.33 4.62 4.74 4.82 0 Qs Q 0 0.150 0.280 0.497 0.680 0.842 0.919 0.973 10 P P max 0.540 0.529 0.484 0.415 0.313 0.247 0.152 Table I : Dimensionless Performance Parameters for full journal bearings with side flow . Q7) a) b) Q8) a) b) SECTION - II UNIT - IV Derive relation for flow rate of lubricating oil and load carrying capacity for a Circular step Bearing with neat sketch. [8] Two reservoirs are connected by a slot 20 cm wide, 0.3 mm thick and 30 cm long. The reservoirs are filled with oil of 105cP. The pressures in the two reservoirs are 10 bar and 3 bar respectively. Determine the quantity of oil flowing. Assume relative density of 0.8. [8] OR Discuss different types of energy losses in hydrostatic bearings & derive an equation for the same. [8] The hydrostatic step bearing consists of six pads as shown. Neglecting the flow over corners of each pad can be approximated as a circular area of outer and inner diameter of 500 mm and 200 mm resp. The total thrust load is 900 KN and the film thickness is 0.15mm. The viscosity and density of the oil are 30 cP and 0.9 gm/cc resp. The specific heat of the lubricant is 2.09 KJ/kg oC. If the shaft is rotating at 720rpm, calculate. i) Supply pressure, ii) Lubricant flow rate, iii) Frictional power loss, iv) Pumping power loss and, v) Temperature rise. [8] [3864] - 155 -3- Q9) a) b) Q10)a) b) Q11)a) UNIT - V Derive equations for load carrying capacity and time of approach for a rectangular plate near a plane under hydrostatic squeeze film Lubrication. [10] Explain merits, demerits and applications of Gas bearings. [6] OR Explain the mechanism of squeeze film lubrication. Where does it occur? [8] Two parallel plates 3 cm long and infinitely wide are separated by oil of viscosity 0.6 Ns / m2 and are approaching each other. If a load of 30 KN per meter width is applied, what will be the film thickness after one second? Initial film thickness is 25 m. [8] UNIT - VI Derive an expression for load carrying capacity of Rayleigh step bearing which has entry zone gap of h1 over a length of B1 and exit zone gap of ho over a length of B0 and sliding with a velocity of U. [10] h1 h = 1 . 87 and 0 b) Q12 a) b) c) B1 = 2 . 588 B0 Discuss the mechanism of elasto - hydrodynamic lubrication and give its applications. [8] OR Write a short note on (Any Two) :[6] i) Plastic bearing materials. ii) Sintered Metal bearings. iii) Bi and Tri metal bearings. Explain different types of gaskets and oil seals in brief. [6] Explain different patterns of oil grooves in case of sliding contact bearings. [6] [3864] - 155 ***** -4-

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