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2003 Course Design Eng.

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Total No. of Questions : 12] P1150 [Total No. of Pages : 5 [3664]-141 B.E. (Mech. S/W) DESIGN ENGINEERING (2003 Course) Time : 4 Hours] [Max. Marks : 100 Instructions to the candidates:1) Answer three questions from Section - I and three questions from Section - II. 2) Answers to the two sections should be written in separate books. 3) Neat diagrams must be drawn wherever necessary. 4) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 5) Assume suitable data, if necessary. SECTION - I Q1) a) A pair of straight bevel gears mounted on shafts, which are intersecting at right angle consists of 24 teeth pinion meshing with 32 teeth gear. The pinion is connected to 7.5 kW, 1000 rpm electric motor. The starting torque of the motor is 125% of the rated torque. The load distribution factor is 1.2. The gear is made of gray cast iron FG 350, while the pinion is made of case hardened 40 C8 (Sult = 580 N/mm2). The gears are generated. Tooth system is 20 full depth involute. i) ii) If the factor of safety required against bending failure is 3.0, design the gear pair by using velocity factor. If the factor of safety required against pitting failure is 2.0, specify the surface hardness required on the gears. Velocity factor = 5.6 5.6 + v Lewis form factor = 0.484 2.87 Z Std module (mm) : 1, 2, 3, 4, 6, 8, 10, 12, 15 [12] P.T.O. b) A worm transmits 3kW at 1440 rpm and drives a gear having 60 teeth. The pitch circle diameter of worm is 90 mm and is triple threaded. The module of the worm gear is 4 mm. Calculate [6] i) Tangential force on the worm and gear. ii) Separating force. iii) Efficiency of the drive. Assume coefficient of friction to be 0.1 and wheel to have a normal pressure angle of 20 . OR Q2) a) A worm gear pair is used to transmit 3.7 kW power from an electric motor running at 1000 rpm to a machine. The worm is quadruple threaded, while the worm gear has 52 teeth. The module is 8 mm and the diametral quotient of the worm is 10. The face width of the gear is 58 mm. The worm is made of 10C4, while the gear is made of phosphor bronze having permissible bending stress of 80 N/mm2. The wear load factor for worm gear is 0.6 N/mm2. The transverse pressure angle is 21.4 . The coefficient of friction between the worm and worm gear teeth is 0.035. The application factor is 1.25. The external surface area of the housing is 1.35 m2. The overall heat transfer coefficient is 18W/m2 C. Determine : i) Factor of safety against bending, & pitting failure. ii) Temperature rise of lubricating oil. Lewis form factor, y = 0.484 2 .87 . Z9 [12] b) A 21 teeth straight bevel pinion rotating at 720 rpm transmits 10 kW power to a 40 teeth bevel gear. The module is 6mm and the pressure angle is 20 face width is 45 mm. If the shaft angle is 90 , determine the components of force acting on meshing teeth. [6] Q3) a) A tube of inner and outer diameters 20 mm and 40 mm respectively is reinforced by shrink fitting another tube of diameter 60 mm. This assembly is to withstand an internal pressure of 10MPa. The shrinkage is such that the maximum tangential stress in both the tubes is same. Calculate the contact pressure and the dimensions of the tube. Also plot the important values of resultant stresses. [12] Describe various supports used for vertical pressure vessel. [4] b) OR [3664]-141 2 Q4) a) b) Q5) a) b) A class 2 cylindrical pressure vessel of 1220 mm inner 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 of vessel are 30 mm and 15 mm respectively. The corrosion allowance is 1.5 mm. Double welded butt joints which are spot radiographed are used for fabrication. Nozzle is made of seamless tube. The pressure inside the vessel is 2 MPa. Allowable stresses for shell and nozzle are 120 MPa and 100 MPa respectively. A reinforcing pad of 6 mm thickness and 350 mm outside diameter is used. Find wheather [12] reinforcement is required and if not suggest necessary action. Explain different types of welded joints used in pressure vessels. [4] An assembly comprises of three components A, B and C as shown in figure. The mean dimensions of components A, B and C are 25, 15 and 20 respectively. Component C has three times and B has two times the standard deviation of component A. The overall dimensions and the individual dimensions are normally distributed. The natural tolerance and design tolerance are equal. Specify the tolerances for individual components. [10] Explain various junction designs with relation to castings. [6] OR Q6) a) b) Explain design principles in welding. [6] A machine member made of plain carbon steel has a mean yield strength of 250 MPa and deviation of 30MPa. This member is subjected to a bending stress with a mean of 160 MPa and a standard deviation of 15 MPa. Determine [10] i) Probability of failure and reliability of the machine member. ii) Minimum factor of safety available. iii) Average factor of safety available. Assume normal distribution. Standardised variable Z and area under the graph is Z A [3664]-141 1.0 0.3413 2.0 0.4772 2.5 0.4938 3 3.0 0.4987 SECTION - II Q7) a) b) A cantilever beam of circular cross section is fixed at one end and subjected to completely reversed force of 10 kN at the free end. The force is perpendicular to the axis of the beam. The distance between free and fixed ends is 100 mm. The beam is made of steel with ultimate tensile strength of 540 N/mm2 and tensile yield strength of 320 N/mm2. Neglect the effect of stress concentration. The size factor, surface finish factor and reliability factors are 0.85, 0.8 and 0.868 respectively. Temperature factor is 1.010. If the diameter of the beam is 35 mm, find the life of the beam. [12] Explain Miner s equation. [6] OR Q8) a) b) Explain different endurance limit modifying factors. [6] A transmission shaft made of steel having ultimate tensile strength of 630 MPa and yield point strength of 360 MPa respectively is subjected to a fluctuating torque which varies from 600 Nm clockwise to 100 Nm anticlockwise direction. The surface finish factor and size factor are 0.8 and 0.85 respectively. Reliability factor is 0.897. If the factor of safety is 2 find the diameter of the shaft. Use distortion energy theory of failure. Use modified Goodman diagram. [12] Q9) a) In a light weight equipment, a shaft is transmitting a torque of 900 Nm is to have a rigidity of 90 Nm/degree. Assume a factor of safety of 1.5 based on yield strength. Design the shaft with minimum weight. What will be the change in design for minimum cost. Assume maximum shear stress theory of failure. Use the following data for the materials.[12] Material M1 8500 16 130 80 M2 3000 32 50 26.7 M3 4800 480 90 40 M4 b) Mass density (kg/m3) Material cost Yield strength Shear modulus (Rs./N) (MPa) (GPa) 2100 32 20 16 Explain Johnson s method of optimum design. OR [3664]-141 4 [4] Q10)A cantilever beam of length 200 mm and rectangular cross section is to function in a device as a spring member. The width is five times its depth. It is subjected to a vertical force which varies from +500 N to 500 N at its free end. The maximum deflection at the free end is limited to 1 mm. The factor of safety is 2. Design the beam for minimum material cost out of the following materials. [16] Material Mass density Material cost Endurance Modulus of elasticity (kg/m3) (Rs./kg) limit (MPa) (MPa) M1 7800 20 130 207 103 M2 2800 70 50 72 103 M3 4500 800 260 114 103 Q11)a) An inclined conveyor handles an ore having density of 1.5 t/m3. The material has to be conveyed over a distance of 2 kms and height of 450 m. If the belt speed is to be 120 m/min, then find the standard width of four ply belt so that the material can be conveyed at a rate of 3 tonnes/hr. for the inclined belt use following data. Conveyor inclination 16 20 21 25 Flowability factor b) 10 15 2.65 10-4 2.5 10-4 2.35 10-4 Standard belt widths are 300, 500, 600, 800, 1000, 1200, 1400, 1600, 1800 mm. Also determine the diameter and width of the drive pulley and the gear reduction ratio for the motor if the motor speed is 1440 rpm. Assume the material for the ply of belt has material factor = 2.5 and belt tension & arc of contact factor = 80. [12] Explain advantages of belt conveyors over other conveyors. [4] OR Q12)a) b) Explain different types of belt conveyor layouts. [6] Determine the resistance offered by a single carrying & return idler for the conveyor having following data. Capacity of the conveyor = 400 tph. Belt speed = 2 m/s Mass of belt = 16 kg/m Carrying side pitch = 1m Return side pitch = 2m Coefficient of friction between idler & pulley = 0.02 Coefficient of friction between roller pin and idler = 0.04 Belt inclination = 15 . [10] vvvv [3664]-141 5

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