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2003 Course Design Eng.

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Total No. of Questions : 12] P1318 [Total No. of Pages : 5 [3764]-151 B.E. (Mechanical 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) 3) Answers to the two sections should be written in separate answer books. 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) Annume suitable data, if necessary. SECTION - I Q1) a) A straight bevel pinion having 18 teeth is to mesh with a straight bevel gear having 40 teeth. Pinion and gear are made of case hardened steel having ultimate tensile strengths of 720 MPa and 580 MPa respectively. The gear pair is manufactured by generation. The pinion is connected to 15 kW, 1440 rpm electric motor. The starting torque is approximately twice the rated torque. If the surface hardness of the gear pair is to be 350 BHN, design the gear pair with a factor of safety of 1.5. Assume velocity factor accounts for dynamic load. [12] b) Sketch and describe various arrangements of worm gear reducer. [6] OR Q2) a) A worm gear pair transmits 5 kW power from a shaft rotating at 1440 rpm to another shaft rotating at 36 rpm. The worm gear is made of phosphor bronze and worm is made of 14C6. The normal pressure angle is 20o. The temperature rise of the lubricating oil is limited to 50oC and the overall heat transfer coefficient is 18 W/m2 oC. i) Find dimensions of worm and worm gear. ii) Required effective surface area of the gear box approximate centre distance is a 8[(G + 5) Pi]0.588 mm. Where G gear ratio, Pi - input power kW. P.T.O. 1 G 30 40 54 160 1/30/10/8 1/54/10/5 200 1/30/10/10 1/40/10/8 acmm 250 1/40/10/10 Sliding velocity m/s 5 6 7 Coefficient of friction 0.025 0.023 0.022 8 0.0215 [12] b) Derive the equation for virtual number of teeth in case of straight tooth bevel gear. [6] Q3) a) An air receiver consisting of a cylinder closed by hemispherical ends. It has a length equal to two times the diameter of vessel. It has a storage capacity of 0.25 m3 and an operating internal pressure of 5 MPa. It is made of plain carbon steel (Sult = 340 MPa) and factor of safety of 4. Neglecting the effect of welded joints, determine the dimension of the reciever. [6] b) An unfired cylindrical pressure vessel is subjected to an internal pressure of 0.55 MPa at 250 oC. Design the flanged joint with following data. Inner diameter of asbestos gasket = 1200 mm. Gasket factor = 2. Gasket design seating stress = 11 MPa. Allowable tensile stress for bolts at atmospheric condition = 80 MPa. Allowable tensile stress for bolts at operating condition = 75 MPa. Corrosion allowance = 1.5 mm. Find the nominal diameter of bolts. [10] OR Q4) a) Derive Birnie's equation for the thickness of shell related to thick cylinders. [6] Find the diameter of bolts of an hydraulic cylinder for the following data. Pressure of hydraulic fluid = 10 MPa. Internal diameter of cylinder = 40 mm. Thickness of cylinder flange = 10 mm. Thickness of cylinder head = 8 mm. b) [3764]-151 2 -2- Thickness of zinc gasket = 3 mm. Cylinder and flange material is FG 200. Modulus of elasticity for FG 200 = 100 GPa. Modulus of elasticity for zinc = 83 GPa. Number of bolts = 4. Preload in each bolt = 2.8 kN. Bolt material is FeE400. Modulus of elasticity for bolt = 207 GPa. Factor of safety for bolts = 6. State wheather the joint will separate or not. Q5) a) b) [10] Explain with sketches design principles in powder metallurgy. [6] The recommended class of fit for the journal and the bearing of a hydrodynamic bearing is 20 H7e8. The diameters of the journal and bearing are normally distributed. The maximum and minimum clearances are limited to 0.08 and 0.05 mm respectively. Determine the percentage of rejected assemblies. The tolerances in micron are as follows. Diameter mm H7 es 20 + 21 e8 ei es ei 0 - 40 - 73 Areas under std. normal distribution curve for 0 to Z are as follows. Z 1.9 2.0 2.6 2.7 A 0.4713 0.4772 0.4953 0.4965 [10] OR Q6) a) b) Explain with sketches, design principles in forging. [6] It is observed from a sample of 200 pins produced on an automatic machine that their diameters are normally distributed with a mean of 10.5 mm and a standard deviation of 0.02 mm. If the rejection is to be limited to 10 pins, determine the design tolerance. Assume the process to be centered. Refer to table of Z and A given in question 5(b). [10] [3764]-151 3 -3- SECTION - II Q7) a) b) Explain causes of stress concentration. [4] Explain repeated stress and completely reversed stress with diagrams.[6] c) Q8) a) b) Q9) a) A plate made of steel (Sult - 580 MPa) is subjected to a completely reversed axial force of 40 kN. The theoretical stress concentration factor at the change of cross section is 2.27 and the notch sensitivity is 0.8. The surface finish factor and the size factor are 0.75 and 0.85 respectively. The load factor is 0.923. The expected reliability is 90% for which the reliability factor is 0.897. If the required factor of safety is 2, find the plate thickness for infinite life. [8] OR Explain methods of reducing stress concentration with diagrams. [6] A mechanical component is subjected to following bending stress cycle. 350 MPa for 70 % time. i) 500 MPa for 5 % time. ii) 6 3V 300 MPa for remaining time.M iii) A = 2 , A = The component is made of plain carbon steel bd = 660 MPa). If the bd 2 (Sult endurance limit is 280 MPa find the life of component. [12] A beam of rectangular cross section is subjected to a maximum bending moment M and a maximum shear force V. The allowable stresses in bending and shear are A an A respectively. Where b and d are the width and depth of cross section of beam. It is desired that the depth of the beam shall not exceed twice its width. Formulate the design problem for optimisation with the objective of minimum cross sectional area of the beam using following data. M = 40 kNM V = 150 kN A = 10 MPa A = 2 MPa Determine the range of optimum dimensions for the cross section of beam. [12] [3764]-151 4 -4- b) Q10)a) Explain the case of normal specifications in optimum design. [4] OR A helical compression spring of an exhaust valve operates under following conditions. i) The force acting on the spring at its extended position should have a specific value of Pmin. ii) The stress at the most compressed position should not exceed max which is permissible torsional shear stress. Neglecting inactive coils, design the spring for minimum weight. [8] b) Q11)a) The initial preload for a helical compression spring is 675 N. The maximum spring load is limited by permissible torsional shear stress of the spring wire, which is 750 MPa. Due to space limitations, the outer diameter of the spring should not exceed 50 mm. Specify the spring dimensions for minimum weight. [8] Explain basic types of product forms with diagram. [6] b) State the important properties to be considered in the design of material handling equipment for unit loads. [4] c) A flat horizontal belt conveyor is used for transporting crushed rock having a mass density of 2 t/m3. The belt is 800 mm wide and has a speed of 1.75 m/s. Determine the capacity of the conveyor. The surcharge angle may be taken as 25o. The effective width b in meters is given by b = 0.9B - 0.05. Where B - belt width, m. [6] Q12)a) OR What is Qualitative display? What are the design recommendations for the Qualitative display. [6] b) Explain with sketch straight roller idler with rolling contact bearing.[4] c) Explain conveyor belt sag in belt conveyors. State equations for carrying and return idlers. [6] [3764]-151 5 -5-

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