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Mechanical System Design (October 2010)

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Total No. of Questions : 12] [Total No. of Pages : 7 P1033 [3864]-131 B.E. (Mechanical) MECHANICAL SYSTEM DESIGN (2003 Course) (402041) Time : 4 Hours] [Max. Marks : 100 Instructions to the candidates: 1) 2) 3) 4) 5) 6) Answer three questions from section-I and three 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, electronic pocket calculator is allowed. Assume suitable data, if necessary. SECTION - I Unit - I Q1) a) Fill in the blanks with proper alternative and rewrite the sentences. [5] 1. For a thick cylindrical tube, open from both the sides, subjected to internal pressure, stress is zero. A) B) C) 2. In case of a shell, hoop and longitudinal stresses are equal. A) B) C) 3. Cylindrical. Ellipsoidal. Spherical. equation is used for designing cylinders with close ends and made of ductile material. A) B) C) 4. Hoop. Longitudinal. Radial. Birnie s. Clavarino s. Lame s. Corrosion allowance will be maximum in case of vessel. A) B) C) Class I. Class II. Class III. P.T.O. 5. Pressure cooker can be called as Pressure Vessel. A) Thick. B) Thin. b) Give two examples each of Externally Pressurized Vessel , Thin Pressure Vessel and Class I Pressure Vessel . [3] c) A high pressure cylinder consists of steel tube with inner and outer diameters of 30mm and 50mm respectively. It is jacketed by outer steel tube with an outer diameter 70mm. The tubes are assembled by shrinking process in such a way that maximum principal stress induced in any tube is limited to 110N/mm2. Calculate the interference pressure and original dimensions of tubes. Assume E = 207000 N/mm2. [8] OR Q2) a) What is the necessity of pre-stressing a cylinder? Explain how Auto-frettage provides necessary pre-stressing for cylinder. [6] b) A cylindrical pressure vessel of 1400mm ID is provided with a nozzle of 250mm inner diameter and 15mm thickness. Protruding lengths of nozzle inside and outside the vessel are 15mm and 50mm respectively and it is made up of seamless tube. The thickness of shell is 20mm. Internal pressure in the shell is 4MPa. The corrosion allowance is 2mm. Permissible tensile stress for shell and nozzle material is 200MPa. Design the dimensions of reinforcing pad if required. The reinforcing material is of same quality as that of the shell and is available in thickness of 18mm. (Assume weld efficiency as 90%) [10] Unit - II Q3) a) Define Optimum design . What is its objective? How the problems of Optimum Design are classified? Elaborate with suitable examples. [6] b) A tensile bar of length 500mm is subjected to constant tensile force of 3000N. If the factor of safety is 2, design the bar diameter, using Johnson s method, with the objective of minimizing material weight using optimum material from the list given in Table 1. [10] Material Density ( ) kg/m3 Cost (c) Rs/kg Syt N/mm2 Steel 7800 28 400 Aluminum Alloy 2800 132 150 Titanium Alloy 4500 2200 800 Table 1. [3864]-131 2 OR Q4) From the manufacturing considerations, if the cross sectional area of the bar to be designed in problem from Q.3(b) above should not be less than 20mm2. Design the bar diameter with the objective of minimizing material cost using other parameters same as given in Q.3(b) above. [16] Unit - III Q5) a) Derive expression for bending stress in flywheel arm due to torque transmission. [6] b) Torque produced by a four stroke engine is given by T = 5000 + 750 sin + 2000 sin 2 Nm where is angle turned by the crank shaft. Mean engine speed of 130 rpm is to be allowed to fluctuate by 3%. Load torque is constant. Design rim cross section of the flywheel made up of wheel material is FG 150 ( = 7000kg/m3), use factor of safety as 5. Maximum size of flywheel is limited 2m. Assume Rim width to thickness ratio as 2. Assume that rim contributes 90% of the total required inertia. [12] OR Q6) a) What are the different stresses those can possibly be developed in Flywheel Rim and Arms? With the help of sketch explain how and why each stress gets developed. State assumptions made in each case. Even tough disc type flywheel is easy for manufacturing, why rimmed flywheels are preferred? [6] b) The turning moment diagram of four stroke engine can be assumed to be consisting of four triangles. The areas measured are 750, 100, 80 and 200mm 2 f or power, exhaust, suction and compression strokes respectively. Scale chosen for plotting the diagram is 1mm2 = 10 J. The engine is running at 700rpm and speed fluctuation is to be kept within 2% of mean speed. Wheel material is FG 150 ( = 7000 kg/m3) with factor of safety as 4. The wheel diameter is limited to 1m and rim is to have rectangular cross section with width to thickness ratio of 2. Design the Flywheel if rim contributes 90% of required MI. Allowable shear stress for flywheel shaft can be taken as 50 N/mm2. [12] [3864]-131 3 SECTION - II Unit - IV Q7) a) The bolt diameters are normally distributed with a mean of 10.015mm and a standard deviation of 0.02mm. The tolerance specified by designer for bolt diameter is 10 0.03mm. Calculate the percentage of bolts likely to be rejected. (Refer Table 2 for Areas below normal distribution curve) b) Write a short note on : Design for Powder Metallurgy. [10] [6] OR Q8) a) A shaft and hole assembly have following dimensions : [10] Shaft dia = 50 0.18mm Hole dia = 50.2 0.24mm Assuming the shaft and hole diameters are normally distributed, determine the probability of interference fit. (Refer Table 2 for Areas below normal distribution curve) b) Write a short note on : Design for Casting. [3864]-131 4 [6] Unit - V Q9) a) With the help of appropriate sketch explain why : [6] 1) The distance between adjacent fixed gears in a multi-speed sliding mesh gear drive must be greater twice of the face width of gears. 2) The difference in number of teeth on adjacent gears on a compound gear from multi-speed sliding mesh gear drive must be greater than four. b) Figure 1 shows gearing diagram of a multispeed gearbox with number of teeth on each gear as specified. Motor M , running at 1435 rpm, is driving the input shaft through flat belt running over the pulleys with specified diameters. The lowest speed of gearbox should be near about 100 rpm. Answer the following questions based on the figure. (All Gears are having same module) [12] 1) 2) Enlist the speeds available on output shaft. 3) Draw speed diagram of the gearbox. 4) What is the geometric progression ratio and range ratio of the gearbox? 5) Write structural formula of the gearbox. 6) What is the current (Meshing A-P D-S) output speed of the gearbox. 7) [3864]-131 Calculate Number of teeth T1 (Round off the calculated number T1 to nearest integer) and accordingly calculate T2. What will be the output speed if meshing is B-Q C-R. 5 OR Q10) A multi-speed gear box is to be designed for a machine tool for speeds varying between 50 rpm and 500 rpm. Recommended GP ratio is as per R5. It is to be driven by an electric motor running at 750 rpm and fitted with 115mm diameter flat belt pulley. Input shaft of gear box is fitted with corresponding flat belt pulley of 545mm diameter. For the proposed system, List out intermediate speeds and round them off to the nearest multiple of 5. Write all structure formulae. Draw symmetric structure diagrams based on short listed formulae. Select optimum structure diagram. Draw speed diagram. Draw gearing diagram when third speed from bottom is being tapped. Find out number of teeth on each gear assuming min. no of teeth as 20. Draw deviation diagram of the system. [18] Unit - VI Q11) a) Answer the following in brief with the help of supporting sketches (if required) [6] 1. What is the need of containerization? 2. What are different types of conveyors? 3. What is meant by troughed belt conveyor? What is its advantage over flat belt conveyor? b) What is the use of following components in a flat belt conveyor? 1. Snub Pulley. 2. Scraper. 3. Tension take up device. 4. [4] Bend Pulleys. c) An inclined belt conveyor with 20o inclination is to be used for transporting bulk material with specific weight 10000 N/m3 Belt width is 1000mm and belt speed is 2m/s. If flow factor is 2.5 10 4, find out capacity of conveyor. [6] OR [3864]-131 6 Q12) Following data relate to a horizontal belt conveyor used for conveying coal in a thermal power station : [16] Capacity of conveyor : 600 ton/hr Density of coal : 800 kg/m3 Belt speed : 2m/s Surcharge factor : 0.15 Number of plies : 3 Material Factor K1 : 2 Belt tension and contact factor : 80 Material conveying length : 260m Center distance between snub pulleys : 255m Ratio of tail pulley to drive pulley dia. : 1.0 Ratio of snub pulley to drive pulley dia. : 0.5 Mass of each carrying run idler : 25kg Mass of each return run idler : 20kg Pitch of carrying run idlers : 1m Pitch of return run idlers : 2.5m Friction factor for idlers : 0.02 Snub Factor for snub pulleys : 0.03 Snub factor for drive and tail pulleys : 0.06 Material velocity component along belt drive : 1m/s Angle of lap on drive pulley : 210o Coefficient of friction between belt and pulley : 0.4 UTS of belt per meter for ply = 60 N/mm Drive efficiency : 93% Mass of belt per mm width per meter length = 0.0155kg/mm/m Motor speed 1440 rpm Standard Motor ratings : in multiple of 2.5kW from 5 to 25kW Determine following parameters of the conveyor : Standard belt with rounded off to nearest hundred mm. Reduction ratio of the gear reducer Power required to drive the conveyor. xxxx [3864]-131 7

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