ANNA UNIVERSITY , ENGINEERING DESIGN, Semester V
PART – A (10 x 2 = 20 Marks)
1.Suggest suitable materials for the following machine elements and justify the selection.
(a)Pistons of I.C. Engines
(b)Connecting rod used in Automobiles
2.A bush of outer diameter 100mm is to be press fitted to a housing suggest a suitable fit and give the limits of dimensions for the bush and housing.
3.What is the significance of notch sensitivity factor?
4.What is meant by Wahl’s stress factor? Why is it used in the design of helical springs?
5.List the advantages and disadvantages of helical gears.
6.What is the significance of pressure angle in a gear drive?
7.Enumerate the purpose of fly wheels in I.C. Engines and in presses.
8.What are the steps to be taken to reduce the deflection of a power transmission shafts?
9.Explain the use of stability chart in journal bearings.
10.What is meant by Dynamic load rating of a rolling element bearing?
PART – B (5 x 16 = 80 marks)
11. A shaft is supported on two bearings A and B, 800mm between centers. A 20° straight tooth spur gear having 600mm pitch diameter is located at 200mm to the right of the left hand bearing A, and a 700mm diameter pulley is mounted at 250mm towards the left of bearing B. The gear is driven by a pinion placed adjacent to it such that the tangential force acts downward power is taken off from the pulley by a horizontal belt having an angle of lap of 1800. The pulley weighing 3000 N also server as a flywheel. The ratio of belt tensions is 3. If the shaft receives 25 kw at 500 rpm and the permissible shear strength of the material of the shaft is 70 N/mm2 design the shaft, assuming shock and fatigue factors under bending and torsion to be respectively 2.0 and 1.5.
12.a)i) Distinguish between short and long columns. What formula is used in each case?
ii) Find the buckling load for a column having a circular cross-section 15mm in diameter and 215mm long using a safety factor of 3. Each end is welded to a rigid support. The youngs modulus is 205 GPa and yield stress is 99.3 Mpa. Justify your use of the long or short column buckling formula.
12.b) A bolt is subjected to a direct load of 25 kN and a shear load of 15 kN. If the material of the bolt is C15 having an yield strength of 200 N/mm2 determine the size of the bolt using the following theories of failure
(i) Maximum principal stress theory
(ii) Maximum shear stress theory and
(iii) Von Mises (Energy of Distortion) theory
Comment on the results obtained.
13.a) Design a suitable spring for the exhaust value of a petrol engine. The spring should be capable of exerting a net force of 360 N when the value is open and 220 N when it is closed. The maximum inside diameter of the spring is 25mm. The compression in the spring is 8mm. Assume yield stress of the material of the spring to be 665 N/mm2 and modulus of rigidity 8 x 104 N/mm2.
13.b) A single cylinder four stroke gas engine develops 30 kw at 300 rpm. The work done by the gases during the expansion stroke is three times the work done on the gases during the compression stroke. The work during suction and exhaust strokes may be neglected. If total fluctuation of speed is ± 2% of mean speed, design a suitable flywheel.
14.a) A sleeve bearing of diameter 50mm and length 50mm is with SAE 30 oil at an inlet temperature of 60°C. The bearing supports a load of 3 kN and has a journal speed of 1440 rpm. The radial clearance is 0.045 mm. Determine
(i) The temperature rise
(ii)The average temperature of the lubricant
(iii)Coefficient of friction
(iv)Minimum film thickness
(v) Side flow and
14.b) A bearing supports a power transmitting shaft of diameter 40 mm. The radial load coming on the bearing is 3000 N and the axial thrust 4500 N. If the shaft is subjected to light impact and rotates at 400 rpm select a suitable anti friction bearing. Assume that the expected life of the bearing is 10,000 hours.
15.a)A hardened steel worm rotates at 1440 rpm and transmits 12.5 kw to a phosphor bonze gear with a gear ratio of 15. Design the worm gear drive and calculate the heat generated. What is the power lost due to friction?
15.b)The first stage reduction in an automobile gear box is obtained by a helical gear pair. If the reduction ratio is 2.24 and the pinion transmits 45 kw at 4500 rpm, design the helical gear pair assuming a helix angle of 25°.