JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS - II Previous Question Paper (August - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Enumerate the factors that influence most the formation and maintenance of the thick oil film in hydrodynamic bearings?
Answer
The formation and maintenance of a thick oil film in hydrodynamic bearings depend on the following primary factors:
- Relative Velocity: The journal must rotate at a sufficient speed to generate the necessary hydrodynamic pressure to support the load.
- Lubricant Viscosity: The viscosity of the oil must be appropriate to maintain the film under operating temperatures and pressures.
- Bearing Geometry: The radial clearance between the journal and the bearing must be precisely maintained to allow for the wedge effect.
- Load Magnitude: The applied radial load must not exceed the load-carrying capacity generated by the hydrodynamic pressure.
- Surface Finish and Alignment: Proper alignment and smooth surface finishes prevent local metal-to-metal contact and ensure uniform pressure distribution.
A 360o hydrodynamic bearing operates under the following conditions: radial load = 50 kN, journal diameter = 150 mm, bearing length = 150 mm, radial clearance = 0.15 mm, minimum film thickness = 0.03 mm, viscosity of lubricant = 8 cP. What is the minimum speed of operation for the journal to work under hydrodynamic conditions?
Answer
Given: Load W = 50,000 N, Diameter d = 150 mm, Length l = 150 mm, Radial clearance c = 0.15 mm, Minimum film thickness h0 = 0.03 mm, Viscosity μ = 8 cP = 0.008 Ns/m2.
First, calculate the eccentricity ratio ε:
Using the Raimondi and Boyd charts for a full journal bearing (L/D = 1), the Sommerfeld number (S) corresponding to ε = 0.8 is approximately 0.063.
The Sommerfeld number formula is:
Where P = W / (l * d) = 50,000 / (150 * 150) = 2.22 N/mm2 = 2.22 * 106 N/m2, and r/c = 75 / 0.15 = 500.
Substituting the values:
Solving for N (speed in rpm):
The minimum speed required is approximately 4196 rpm.
Design a journal bearing for a centrifugal pump running at 1440 rpm. The diameter of the journal is 100 mm and load on each bearing is 20 kN. The factor ZN/p may be taken as 28 for centrifugal pump bearings. The bearing is running at 75oC temperature and the atmosphere temperature is 30oC. The energy dissipation coefficient is 875 W/m2/oC. Take diametric clearance as 0.1 mm.
Answer
Sign in to view the complete answer paper.
What is the criterion for static load carrying capacity of ball bearing?
Answer
Sign in to view the complete answer paper.
How do you express the life of a bearing? What is an average or median life?
Answer
Sign in to view the complete answer paper.
A ball bearing subjected to a radial load of 3000 N is expected to have a satisfactory life of 10000 h at 720 rpm with a reliability of 95%. Calculate the dynamic load carrying capacity of the bearing, so that it can be selected from a manufacturer’s catalogue based on 90% reliability. If there are four such bearings, each with a reliability of 95% in a system, what is the reliability of the complete system?
Answer
Sign in to view the complete answer paper.
Design a cast iron piston for a single acting four-stroke diesel engine with the following data: Cylinder bore = 300 mm, Length of stroke = 450 mm, Speed = 300 rpm, Indicated mean effective pressure = 0.85 MPa, Maximum gas pressure = 5 MPa, Fuel consumption = 0.30 kg per BP per h, Higher calorific value of fuel = 44,000 kJ/kg. Assume suitable data if required and state the assumptions you make.
Answer
Sign in to view the complete answer paper.
What is the manufacturing method for connecting rod? Why I cross-section is preferred for designing connecting rod?
Answer
Sign in to view the complete answer paper.
Explain the various stresses induced in the connecting rod.
Answer
Sign in to view the complete answer paper.
What is the Wahl factor? Why is it used?
Answer
Sign in to view the complete answer paper.
Is required to design a V-belt drive to connect a 7.5 kW, 1440 rpm induction motor to a fan, running at approximately 480 rpm, for a service of 24 h per day. Space is available for a centre distance of about 1 m.
Answer
Sign in to view the complete answer paper.
Write the expressions for static, limiting wear load and dynamic load for spur gears and explain the various terms used there in?
Answer
Sign in to view the complete answer paper.
A pair of spur gears consists of a 20 teeth pinion meshing with a 120 teeth gear. The module is 4 mm. Calculate (i) the centre distance; (ii) the pitch circle diameters of the pinion and the gear; (iii) the addendum and dedendum; (iv) the tooth thickness; (v) the bottom clearance; and (vi) the gear ratio.
Answer
Sign in to view the complete answer paper.