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SPPU Mechanical Engineering (Semester 8)
Mechanical System Design
June 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Answer any one question from Q1 and Q2
1 (a) Using neat sketches where required, describe and derive the expressions for the principal stresses in a thin cylindrical pressure vessel with no joints subjected to internal pressure and explain which among them will be the design criterion for determining wall thickness.
8 M
1 (b) Determine the inside diameter of shell and the crown radius of the torispherical heads if the thickness of the shell and the torispherical heads of a cylindrical pressure vessel are 12mm and 16mm respectively. The vessel operating at 2.0 MPa pressure is entirely made of 270N/mm2 yield strength material with weld joint efficiency 0.7 and corrosion allowance of 2mm.
10 M

2 (a) Using neat sketches where required, describe and derive the expressions for the principal stresses in a thick cylindrical pressure vessel with no joints subjected to internal pressure.
8 M
2 (b) The maximum tensile stress induced in a pressure cylinder consisting of an inner cylinder of 300mm ID and 400mm OD is 100N/mm2. The vessel is jacketed by outer cylinder of 500mm OD. Calculate the shrinkage pressure and the difference between the inner cylinder OD and the jacket ID before assembly assuming E=210kN/mm2.
10 M

Answer any one question from Q3 and Q4
3 (a) Explain with neat sketches procedure for design of center crankshaft at top dead center position.
6 M
3 (b) Design an exhaust valve for a horizontal diesel engine using following data:
 Cylinder bore =350 mm Length of stroke =400 mm Engine speed =600 RPM Maximum gas pressure =4.0 N/mm2 Seat Angle =45° Mean velocity of gas through port (vp) =50 m/s For steel valve, k=0.42, σb =50 N/mm2

Determine:
i) Diameter of valve port
iv) Diameter of valve stem
v) Maximum lift of valve
10 M

4 Following data is given for a single cylinder four stroke diesel engine:
 Cylinder bore =100 mm Length of stroke =125 mm Speed =2000 RPM Brake mean effective pressure =0.65 MPa Maximum gas pressure =5 MPa Fuel consumption =0.25 kg per BP per h Higher calorific value of fuel =42,000 kJ/kg

Assume that piston transmits 5% of total heat developed in cylinder. Permissible stress of piston material is 37.5 N/mm2 (k=46.6 W/m/°C). Temperature difference between center and the edge of piston head is 220°C.
i) Calculate thickness of piston head by strength consideration
ii) Calculate thickness of piston head by thermal consideration
iii) Decide on the criteria that decides piston head thickness
iv) Decide if ribs are required
v) If yes, calculate number and thickness of piston ribs
vi) Decide whether a cup is required at the top of piston head
vii) If yes, calculate radius of cup.
16 M

Answer any one question from Q5 and Q6
9 M
5 (b) An exhaust valve mechanism helical coiled spring is initially compressed with a preload of 500N and the valve lift is 40mm. Design the spring with modulus of rigidity 90GPa and Wahl's shear stress factor as 1.14 such that the torsional shear stress in spring will not exceed 700 MPa. The spring would weigh minimum with the condition Pmax=2Pmin and have the outside diameter fixed at 60mm when optimized.
10 M

6 M
6 (b) Design a tensile bar of 200 mm length to carry 5 kN tensile load that would cost the least among the following candidate materials:
 Material Density (kg/m3) Cost (Rs/N weight) Syt (MPa) Steel 7500 16 130 Al alloy 3000 32 50 Ti alloy 4800 480 90 Mg alloy 2100 32 20
10 M

Answer any one question from Q7 and Q8
7 (a) Describe design considerations in controls using neat sketches.
8 M
7 (b) Two components A and B are assembled with the overall dimension 40±0.9mm as shown in Fig-1. Specify dimensions for component B if the overall dimension as well as individual component dimensions are normally distributed and natural tolerances are equal to design tolerances.

8 M

8 (a) Describe the design principles in welding using neat sketches.
8 M
8 (b) The diameters in a sample of 100 bolts are normally distributed with 10.5mm mean and 0.02 mm standard deviation. Determine the specified tolerances if the process is centered and only 95 bolts are accepted. Draw a neat figure and use Area under the normal curve from 0 to Z as,
8 M

Answer any one question from Q9 and Q10
9 (a) Organize in a tabulated form comparison between different gear box design progressions.
5 M
9 (b) Describe the basic considerations in design of drives.
5 M
9 (c) Draw the structure diagram and gear box arrangement for following equations of a six speed gear box:
i) z = 2(1) 3(2),
ii) z = 2(3) 3(1),
iii) z = 3(1) 2(3),
iv) z = 3(2) 2(1).
6 M

10 A two stage, nine speed gear box is connected to a motor running at 720 RPM through a belt drive. The gear box is to have a minimum speed of 31.5 RPM and a maximum speed of 500 RPM. Using standard spindle speeds,
a) Draw the structure and speed diagram
b) Draw the gear box layout
c) Determine the number of teeth on each gear
d) Draw percentage deviation diagram and check if design is within permissible limits.
e) Select diameter of pulleys for belt drive based on R20 series with diameter beginning from 80mm.
16 M

Answer any one question from Q11 and Q12
11 (a) Describe in detail belt conveyers and their types using neat sketches.
6 M
6 M
11 (c) A horizontal belt conveyor transports material of mass density 1200 kg/m3. The surcharge factor for the flat belt drive is 0.16 and the belt width is 650mm. Determine the capacity of the conveyor if the belt speed is 1.75m/s and the effective width b(in meters) of the material carried by the belt safely is given by the equation: b = 0.9B-0.05; where B is the belt width in meters.
6 M

12 (a) Explain the basic principles in selection of material handling equipment.
5 M
12 (b) Describe different types of idlers and their characteristics using neat sketches.
5 M
12 (c) Design a belt conveyor to carry material at the rate of 30×103kg/hr with the following details. Bulk density of material is 800kg/m3, angle of bulk material surcharge is 15°, belt speed is 10 km/hr, belt has 4 plies, material factor k 1 for plies is 2.0, belt tension and arc of contact factor k2 is 63. Determine:
i) Suitable belt width
ii) Drive pulley diameter and length
8 M

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