JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS II Previous Question Paper (February/March - 2022 - R16)
Answer any five questions. All questions carry equal marks.
Main
Distinguish between rolling contact bearing and sliding contact bearing.
Answer
Rolling contact bearings and sliding contact bearings differ primarily in their mechanism of friction and operational characteristics:
- Friction: Rolling contact bearings use rolling elements (balls or rollers) to reduce friction, whereas sliding contact bearings rely on a thin film of lubricant to separate the sliding surfaces.
- Starting Friction: Rolling contact bearings have very low starting friction, making them suitable for frequent starts and stops. Sliding contact bearings have high starting friction due to metal-to-metal contact before the hydrodynamic film is established.
- Space Requirements: Rolling contact bearings generally require more radial space, while sliding contact bearings are more compact in the radial direction.
- Load Capacity: Sliding contact bearings are better suited for heavy, high-speed, and shock loads compared to rolling contact bearings.
- Maintenance and Life: Rolling contact bearings are standardized and easily replaceable but have a finite fatigue life. Sliding contact bearings can have an infinite life if properly lubricated and maintained, though they are sensitive to dirt and debris.
- Cost: Rolling contact bearings are generally cheaper for mass-produced applications, while sliding contact bearings can be more expensive due to precision manufacturing requirements.
A journal bearing is proposed for a steam engine. The load on the journal is 3 kN, diameter 50 mm, length 75 mm, speed 1600 r.p.m., diametral clearance 0.001 mm, ambient temperature 15.5°C. Oil SAE 10 is used and the film temperature is 60°C. Determine the heat generated and heat dissipated. Take absolute viscosity of SAE10 at 60°C = 0.014 kg/m-s.
Answer
Given: Load (W) = 3000 N, Diameter (d) = 0.05 m, Length (l) = 0.075 m, Speed (N) = 1600 r.p.m., Diametral clearance (c) = 0.0001 m, Viscosity (μ) = 0.014 kg/m-s, Ambient temp (Ta) = 15.5°C, Film temp (Tf) = 60°C.
1. Calculate Sommerfeld number (S) and Coefficient of friction (μf):
2. Heat Generated (Hg):
3. Heat Dissipated (Hd):
Using the formula Hd = C × A × (Tf - Ta), where A = d × l = 0.00375 m2 and C is the heat dissipation coefficient (approx. 280 W/m2°C for ventilated bearings):
Enumerate the factors that influence most the formation and maintenance of the thick oil film in hydrodynamic bearings.
Answer
Sign in to view the complete answer paper.
The thrust of propeller shaft is absorbed by 6 collars. The rubbing surfaces of these collars have outer diameter 300 mm and inner diameter 200 mm. If the shaft runs at 120 r.p.m., the bearing pressure amounts to 0.4 N/mm2. The coefficient of friction may be taken as 0.05. Assuming that the pressure is uniformly distributed, determine the power absorbed by the collars.
Answer
Sign in to view the complete answer paper.
A rolling contact bearing is subjected to the following work cycle: (a) Radial load of 6000 N at 150 r.p.m. for 25% of the time; (b) Radial load of 7500 N at 600 r.p.m. for 20% of the time; and (c) Radial load of 2000 N at 300 r.p.m. for 55% of the time. The inner ring rotates and loads are steady. Select a bearing for an expected average life of 2500 hours.
Answer
Sign in to view the complete answer paper.
Explain how the following factors influence the life of a bearing: (i) Load (ii) Speed (iii) Temperature (iv) Reliability
Answer
Sign in to view the complete answer paper.
A single row angular contact ball bearing number 310 is used for an axial flow compressor. The bearing is to carry a radial load of 2500 N and an axial or thrust load of 1500 N. Assuming light shock load, determine the rating life of the bearing.
Answer
Sign in to view the complete answer paper.
The following data refer to a 4-stroke cycle, single cylinder diesel engine: Suction pressure = 0.095 MPa, Cylinder diameter = 200 mm, Stroke = 200 mm, Ratio of compression = 15, Engine speed = 7450 rpm, Equivalent mass of reciprocating parts 2 N/mm2 of piston area, Ratio of connecting rod length to crank length is 4. Design Nickel steel connecting rod of I section choosing the suitable values for the permissible stresses for the material.
Answer
Sign in to view the complete answer paper.
Determine the dimensions of an I-section connecting rod for a petrol engine from the following data: Diameter of the piston = 110 mm; Mass of the reciprocating parts = 2 kg; Length of the connecting rod from centre to centre = 325 mm; Stroke length = 150 mm; speed = 1500 r.p.m with possible over speed of 2500 rpm; Compression ratio = 4 : 1; Maximum explosion pressure = 2.5 N/mm2.
Answer
Sign in to view the complete answer paper.
What are the advantages and disadvantages of V-belt drive over flat belt drive? Discuss.
Answer
Sign in to view the complete answer paper.
A concentric spring for an aircraft engine valve is to exert a maximum force of 5200 N under an axial deflection of 40 mm. Both the springs have same free length, same solid length and are subjected to equal maximum shear stress of 880 MPa. If the spring index for both the springs is 6, find (i) the load shared by each spring, (ii) the main dimensions of both the springs, and (iii) the number of active coils in each spring. Assume, G = 85kN/mm2 and diametral clearance to be equal to the difference between the wire diameters.
Answer
Sign in to view the complete answer paper.
Write the expressions for static strength, limiting wear load and dynamic load for helical gears and explain the various terms used therein.
Answer
Sign in to view the complete answer paper.
Design and draw a spur gear drive transmitting 30 kW at 400 r.p.m. to another shaft running approximately at 100 r.p.m. The load is steady and continuous. The materials for the pinion and gear are cast steel and cast iron respectively. Take module as 10 mm. Also check the design for dynamic load and wear.
Answer
Sign in to view the complete answer paper.