JNTU B.Tech III PRINCIPLES OF MACHINE DESIGN Previous Question Paper (November/December - 2017 - R13)

A hollow cylindrical chimney is 25m height, 2.5m external diameter and 2m internal diameter. The density of the chimney material is 700 Kg/m³. A horizontal wind pressure of 125 Pa of projected area is acting on the chimney throughout its height. Find a) the maximum and minimum normal stresses induced in the base of the chimney, and b) the limiting value of the wind pressure so that no point in the base is under tensile stress.

A bar of circular cross-section is subjected to alternating tensile forces varying from a minimum of 200 kN to a maximum of 500 kN. It is to be manufactured of a material with an ultimate tensile strength of 900 MPa and an endurance limit of 700 MPa. Determine the diameter of bar using safety factors of 3.5 related to ultimate tensile strength and 4 related to endurance limit and a stress concentration factor of 1.65 for fatigue load. Use Goodman straight line as basis for design.

A shaft is supported on two bearings placed 0.6m apart. The shaft supports a 0.5m diameter pulley, located at 0.25m to the right of the left hand bearing, and the belt drives a pulley located directly below the shaft. Another pulley of 0.4m diameter is located 0.125m to the right of the right hand bearing, and the belt is driven by a pulley located horizontally to the right. The coefficient of friction for the belt drive is 0.3, and the angle of contact may be taken as 180⁰. The maximum tension in the belt on the smaller (0.4 m diameter) pulley is 3.6kN. Assuming permissible shear stress for the shaft material as 42MPa, determine the shaft diameter.

Design a horizontal belt drive for a centrifugal blower, the blower is belt driven at 600 r.p.m. by a 15 kW, 1750 r.p.m. electric motor. The center distance is twice the diameter of the larger pulley. The density of the belt material = 1500 kg/m³; max allowable stress = 4 MPa; μ₁ = 0.5 (motor pulley); μ₂ = 0.4 (blower pulley); peripheral velocity of the belt = 20 m/s. Determine the following:

1. Pulley diameters
2. Belt length
3. Cross-sectional area of the belt
4. Minimum initial tension for operation without slip
5. Resultant force in the plane of the blower when operating with an initial tension 50% greater than the minimum value.

A pair of straight teeth spur gears is to be transmit 20kW when the pinion rotates at 300rpm. The velocity ratio is 1:3. The allowable static stresses for the pinion and gear materials are 120MPa and 100 MPa respectively. The pinion has 15 teeth and its face width is 14 times the module. Determine: a) Module b) face width and c) Pitch circle diameters of both the pinion and the gera from the stand point of strength only, taking into consideration the effect of the dynamic loading. The tooth form factor y can be taken as y= 0.154-0.912/no. of teeth and the velocity factor Cv = 3/(3+v), where v is in m/s.

A single stage helical gear reducer is to receive power from a 1440 rpm, 25 kW inductions motor. The gear tooth profile is involute full depth with 20⁰ normal pressure angle. The helix angle is 23 degree, number of teeth on pinion is 20 and the gear ratio is 3. Both the gears are made of steel with allowable beam stress of 900MPa and hardness 250 BHN.

1. Design the gears for 20% overload carrying capacity from standpoint of bending strength and wear.
2. If the incremental dynamic load of 8kN is estimated in tangential plane, what will be the safe power transmitted by the pair at the same load.

Design a journal bearing for a centrifugal pump from the following data: load on the journal=20,000N; Speed of the journal=900r.p.m.;type of the oils is SAE 10, for which the absolute viscosity at 55⁰C=0.017kg/m-s; Ambient temperature of oil=15.5⁰C; Maximum bearing pressure for the pump =1.5N/mm². Calculate mass of the lubricating oil required for artificial cooling, if rise of temperature of oil be limited to 10⁰C. Heat dissipation coefficient = 1232 W/m²/⁰C.

Select a suitable deep groove ball bearing for supporting a radial load of 10kN and an axial load of 3 kN for a life of 4000 hrs at 800 rpm. Select from series 63. Calculate the expected life of the selected bearing.