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2003 Course Design Engineering

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Total No. of Questions : 12] P1041 [Total No. of Pages : 5 [3864]-151 B.E. (Mechanical S/W) DESIGN ENGINEERING (2003 Course) Time : 4 Hours] [Max. Marks : 100 Instructions to the candidates: 1) 2) 3) 4) 5) 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. Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. Assume suitable data, if necessary. SECTION - I Q1) A straight bevel pinion having 21 teeth to be made of alloy steel (Sult = 800 MPa) is to mesh with bevel gear made of plain carbon steel (Sult = 720 MPa). The axes of pinion and gear intersect at right angles. The gear pair is required to transmit 13kW power from a spindle running at 500rpm to a machine running at 300rpm. The starting torque of the motor is 110% of the rated torque. The factor of safety is 2.0. Tooth system is 20o full depth involute. The gears are to be machined to meet the specifications of grade 6. The pinion and gear are to be case hardened to 400 BHN and 350 BHN respectively. The deformation factor for gear pair is 10900 e N/mm. Design the gear pair using Buckingham s equation for dynamic load. For grade 6. e = 8 + 0.63 [ m + 0.25 dm ] where dm : is mean diameter in mm. Velocity factor = 6 6+v Std module (mm) 1, 2, 3, 4, 6, 8, 10, 12, 15 OR [18] Q2) A single start worm to be made of case hardened steel is to mesh with worm gear having permissible bending stress of 85 MPa. The wear factor is 0.55 MPa. The ratio of pitch circle diameter of worm to the module is 10. Tooth system is 20o full depth involute. The gear pair is required to transmit 10kW of power from an electric motor running at 1500 rpm to the hoisting drum running at 30 rpm. The application factor and factor of safety are 1.25 and P.T.O. 1.5 respectively. The coefficient of friction between worm and worm gear teeth is 0.05. If the overall heat transfer coefficient is 28 W/m2oC, design the gear pair and find the temperature rise of the lubricating oil above the atmospheric temperature. Standard module (mm), 1, 2, 3, 4, 5, 6, 8, 10, 12, 15 Surface area A = 1.14 10 4 a1.7 m2 a : center distance in mm. [18] Q3) A class 2 cylindrical pressure vessel of 1220 mm inside diameter and 15 mm thickness is provided with a nozzle of 200 mm inner diameter and 12 mm thickness. The extensions of the nozzle outside and inside the vessel are 30 mm and 15 mm respectively. The corrosion allowance is 1.5mm. Double welded butt joints which are spot radiographed are used to fabricate the shell. The nozzle is made up of seamless tube. The pressure inside the vessel is 2 MPa. The allowable tensile stress for shell and nozzle are 120 MPa and 100 MPa respectively. A reinforcing pad of 6 mm thickness and 350 mm outside diameter is welded around the nozzle external to the shell. Find whether reinforcement is adequate or not. Devise the remedy for the same. Draw the diagram of the areas. [16] OR Q4) a) A cylindrical pressure vessel shell of inside diameter 1500 mm is subjected to an internal pressure of 2 MPa. The shell as well as heads are made of low alloy steel with ultimate tensile strength of 450 MPa. The double welded butt joints which are spot radiographed are used to fabricate the vessel. Corrosion allowance is 3 mm. Determine the thickness of the cylindrical shell and thickness of head if the heads are [10] i) ii) iii) iv) Flat. Plain formed. Torispherical with crown radius of 1125 mm. Semi-elliptical with ratio of major axis to minor axis as 2. b) Explain the design of skirt support in case of vertical pressure vessels.[6] Q5) a) Explain design principles in machining. b) A shaft and hole assembly have the following dimensions. [6] [10] Shaft diameter = 40 0.18 mm Hole diameter = 40.2 0.24 mm Assuming the shaft and hole diameters are normally distributed, determine the probability of interference fit between the shaft and hole. [3864]-151 2 Area of the curve from 0 to Z is Z 1.0 1.5 2.0 2.5 A 0.3413 0.4332 0.4772 0.4938 OR Q6) a) Explain various junction designs in case of casting. [6] b) A cantilever beam made of steel having the mean yield strength of 280 MPa and standard deviation of 40 MPa. It is subjected to bending stress [10] with a mean of 180 MPa and a standard deviation of 20 MPa. Determine : i) ii) iii) Reliability of beam. Minimum factor of safety available. Average factor of safety available. The area under the curve is as follows : Z 2.0 2.2 2.4 2.6 A 0.4772 0.4861 0.4918 0.4953 SECTION - II Q7) a) A steel bar of 50 mm diameter is subjected to a completely reversed bending stress of 250 MPa. The ultimate tensile strength is 600 MPa. The surface finish factor and size factor are 0.43 and 0.85 respectively. The reliability factor is 0.897. Assuming there is no stress concentration, determine the life of bar. [8] b) Explain the terms fatigue stress concentration factor and notch sensitivity. [4] c) Explain design for infinite life for fluctuating stresses. [6] OR Q8) A transmission shaft supports a pulley midway between two bearings. The bending moment at the midpoint varies from 200 Nm to 600 Nm. The torque on the shaft varies from 70 Nm to 200 Nm. The frequencies of variation of bending moment and torque are equal to shaft speed. The shaft speed is 1440 rpm. The shaft has ultimate strength of 540 MPa and yield strength of 400 MPa. The corrected endurance limit is 200 MPa. If the factor of safety is 2 find diameter of shaft by modified Goodman method. Use maximum distortion energy theory for calculation of resultant stress. [18] [3864]-151 3 Q9) a) A thin spherical pressure vessel is subjected to an internal pressure of 4 MPa. The mass of empty vessel should not exceed 125 kg. If the factor of safety is 3.0, design the pressure vessel with the objective of maximising the gas storage capacity out of the following materials. Material Sult MPa Density kg/m3 Low alloy steel 500 7800 Aluminium alloy 250 2800 Copper alloy 420 8400 Select the material and find out the dimensions and capacity. b) Explain Johnson s method for optimisations. [12] [4] OR Q10) A simple tensile bar of length 200 mm is subjected to a constant tensile force of 5000 N. If the factor of safety is 3, design the bar with the objective of minimising the material cost, out of the following materials. Material Density kg/m3 Cost per unit mass Rs./kg Yield strength MPa Steel 7800 14 400 Al. alloy 2800 66 150 Ti alloy 4500 1100 800 Mn alloy 1800 75 100 from the manufacturing considerations, the cross sectional area of the bar [16] should not be less than 50 mm2. Q11) a) An inclined conveyor handles an ore having density of 0.5t/m3. The material has to be conveyed over a distance of 1.2km and a height of 500 meters. The belt speed is 1.5 m/s and belt width is 400 mm. Determine the capacity of the conveyor. Conveyor inclination 16o - 20o 21o - 25o 26o - 30o Flowability factor 2.5 10 4 2.35 10 4 2.2 10 4 [8] b) Explain the classification of material handling equipment. [4] c) Draw and explain both end discharge in case of belt conveyor. [4] [3864]-151 4 OR Q12) a) Draw any four types of idlers used in belt conveyor. [6] b) Draw and explain man machine closed system between a driver and motor cycle. [6] c) Determine the belt capacity of a flat horizontal belt if the effective width of the material on the belt is b velocity is v and surcharge angle is 15o. [4] xxxx [3864]-151 5

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