About this previous year paper
MACHINE DESIGN – II (EME602)
SECTION – A
(Attempt All | 10 × 2 = 20 Marks)
(a) Wedge film and squeeze film journal bearings
Wedge film bearing: Load is supported by a pressure wedge formed due to relative motion between journal and bearing.
Squeeze film bearing: Load is supported by pressure developed when lubricant film thickness decreases due to squeezing action, even without rotation.
(b) Journal bearing terms
(i) Bearing characteristic number (Sommerfeld number):
S=μNp(rc)2S=\frac{\mu N}{p}\left(\frac{r}{c}\right)^2S=pμN(cr)2
It indicates performance of a hydrodynamic bearing.
(ii) Bearing modulus:
μNp\frac{\mu N}{p}pμN
It relates viscosity, speed, and bearing pressure.
(c) Bearing life and median life
Bearing life is expressed as the number of revolutions or operating hours until fatigue failure.
Median life (L₅₀): Life at which 50% of bearings survive under given conditions.
(d) Gear tooth failures and remedies
Failures include wear, pitting, scoring, tooth breakage, and corrosion.
Remedies: proper lubrication, correct material selection, surface hardening, accurate alignment, and controlled loading.
(e) Herringbone gear
A herringbone gear is a double helical gear with opposite helix angles on either side.
Use: heavy-duty applications such as marine gearboxes due to zero axial thrust.
(f) Forces acting on worm and worm gear
Tangential force
Axial thrust
Radial (separating) force
These depend on transmitted power, lead angle, and friction.
(g) Types of cylinder liners
Dry liner: Not in direct contact with coolant
Wet liner: Directly in contact with coolant
Semi-dry liner: Partial contact with coolant
(h) Forces induced in connecting rod
Gas pressure force Inertia force due to reciprocating mass
Bending force Buckling force
(i) Function of connecting rod
It transmits motion and power from the piston to the crankshaft and converts reciprocating motion into rotary motion.
(j) Helical gear terms
Helix angle: Angle between tooth direction and gear axis
Normal pitch: Pitch measured normal to the tooth direction
SECTION – B
(Attempt Any Five | 5 × 10 = 50 Marks)
(a) Journal bearing – maximum safe speed
Given data substituted in bearing power loss = heat dissipation capacity condition.
Using Petroff’s equation, maximum safe speed is calculated by equating frictional heat generated to heat dissipated.
(b) Power absorbed by collar bearing
Assuming uniform pressure, frictional torque:
T=23μW(Ro3−Ri3)(Ro2−Ri2)T = \frac{2}{3}\mu W\frac{(R_o^3 - R_i^3)}{(R_o^2 - R_i^2)}T=32μW(Ro2−Ri2)(Ro3−Ri3)
Power absorbed:
P=2πNT60P = \frac{2\pi NT}{60}P=602πNT
(c) Dynamic load rating of ball bearing
Equivalent dynamic load:
Peq=(P1pt1+P2pt2+… )1/pP_{eq} = (P_1^p t_1 + P_2^p t_2 + \dots)^{1/p}Peq=(P1pt1+P2pt2+…)1/p
Using life equation:
L=(CPeq)3L = \left(\frac{C}{P_{eq}}\right)^3L=(PeqC)3
Dynamic load rating C is calculated.
(d) Power transmitted by spur gears (strength basis)
Using Lewis equation:
WT=σbypcW_T = \sigma b y p_cWT=σbypc
Allowable stress of weaker member (bronze pinion) governs design.
Power transmitted is obtained from tangential load.
(e) Helical gear design
Normal module and virtual number of teeth calculated.
Face width = 10m to 14m. Gears checked for:
Static strength Wear strength
(using given σₑₛ)
(f) Worm gear calculations Tangential force
Axial thrust Separating force
Efficiency:
η=tanγtan(γ+ϕ)\eta = \frac{\tan\gamma}{\tan(\gamma+\phi)}η=tan(γ+ϕ)tanγ
(g) Diesel engine cylinder design Using indicated power relation:
IP=pmLAN2IP = \frac{p_m L A N}{2}IP=2pmLAN
Bore and stroke calculated.
Cylinder head thickness and stud size obtained using strength equations.
(h) Variable load on rolling contact bearing
Life equation derived using:
L=(CPeq)pL = \left(\frac{C}{P_{eq}}\right)^pL=(PeqC)p
where equivalent load considers load variation over duty cycle.
SECTION – C
(Attempt Any Two | 2 × 15 = 30 Marks)
3) Full journal bearing – cooling and oil flow
Heat generated: Hg=fWVH_g = f W VHg=fWV
Heat carried away by oil: Hd=mcpΔTH_d = m c_p \Delta THd=mcpΔT
Artificial cooling = Hg−HdH_g - H_dHg−Hd
Oil flow rate obtained from energy balance.
4) Bevel gear design
Steps: Determine module using Lewis equation
Face width = 1/3 pitch cone length Pitch diameters from velocity ratio
Pinion shaft diameter from torsion equation:
T=π16τd3T = \frac{\pi}{16}\tau d^3T=16πτd3
5) Design of cast iron piston
Design includes: Piston head thickness
Piston rings (number and dimensions) Piston skirt length
Piston pin dimensions
Thermal and strength considerations applied using standard design relations.