JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS - II Previous Question Paper (February - 2023 - R18)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions. Assume Suitable data, if necessary.
Part A
What is bearing characteristic number as applied to journal bearing?
Answer
The bearing characteristic number is a dimensionless parameter used to analyze the performance of a hydrodynamic journal bearing. It is defined by the expression:
where Z is the absolute viscosity of the lubricant (in Ns/m2), N is the journal speed (in rpm), and p is the bearing pressure (in N/mm2). It is used to determine the operating regime of the bearing on the Stribeck curve, indicating whether the bearing is operating under hydrodynamic, mixed, or boundary lubrication conditions.
Distinguish between “Hydrodynamic bearings” and “Hydro static bearings”.
Answer
The primary distinction between hydrodynamic and hydrostatic bearings lies in the mechanism used to generate the fluid film pressure required to support the load:
- Hydrodynamic bearings: The fluid film pressure is generated automatically by the relative motion between the sliding surfaces. The geometry of the bearing and the viscosity of the lubricant cause the fluid to be dragged into a converging wedge, creating sufficient pressure to support the load. These bearings require a minimum operating speed to function effectively.
- Hydrostatic bearings: The fluid film pressure is generated by an external high-pressure pump that forces lubricant into the bearing clearance. Because the pressure is supplied externally, these bearings can support a load even when the shaft is stationary, making them ideal for applications involving high starting loads or very slow speeds.
Why are ball and roller bearings called anti friction bearings?
Answer
Sign in to view the complete answer paper.
Enumerate any two advantages and disadvantages of rolling contact bearings to sliding contact bearings.
Answer
Sign in to view the complete answer paper.
What is the function of gudgeon pin?
Answer
Sign in to view the complete answer paper.
Enumerate the design considerations for crank pin.
Answer
Sign in to view the complete answer paper.
What are the advantages of fabric rubber belts?
Answer
Sign in to view the complete answer paper.
Explain the designation of V-belt with the help of examples.
Answer
Sign in to view the complete answer paper.
State two most important reasons for adopting involute curve for a gear tooth profile.
Answer
Sign in to view the complete answer paper.
State any four advantages of gear drive over other types of drives.
Answer
Sign in to view the complete answer paper.
Part B
Explain the design procedure of journal bearing.
Answer
Sign in to view the complete answer paper.
Each bearing of an electrical motor sustains a radial load of 4 kN. Assuming (l/d) ratio of 1.1, determine the length of the bearing, if the permissible bearing pressure is limited to 1 N/mm2.
Answer
Sign in to view the complete answer paper.
Derive Petroffs equation for the co-efficient of friction in a lightly loaded bearing.
Answer
Sign in to view the complete answer paper.
The following data are given for a full hydrodynamic bearing: radial load = 25 kN, journal speed = 900 rpm, unit bearing pressure = 2.5 MPa, (l/d) ratio = 1, viscosity of lubricant = 20 cP, class of fit = H7e7 Calculate: (i) dimensions of the bearing; (ii) minimum film thickness; and (iii) requirement of oil flow.
Answer
Sign in to view the complete answer paper.
The radial reaction on a bearing is 9000 N. It also carries a thrust of 5000N. The speed of the shaft is 1000 rpm. The outer ring is stationary. Expected average life of bearing is about 25,000 hours. The load on the bearing is smooth, the service is 8 hours/day. Select: a) Suitable roller bearing. b) What is the rated 90% life of selected bearing? c) Compute the probability of the selected bearing surviving 25,000 hours.
Answer
Sign in to view the complete answer paper.
A roller bearing is selected to withstand a radial load of 40 kN and life of 1200 hrs at 600 rpm. What load rating would you look for in searching from manufacturers catalogue if it specifies load at speed 500 rpm and life 3000 hrs.
Answer
Sign in to view the complete answer paper.
Select a suitable rolling bearing for a 55 mm diameter shaft. The bearing should be capable of withstanding 3 kN radial and 1.5 kN axial load at 750 rpm. The bearing is to have a desired rated life of 2000 hrs at a reliability of 94%. There is a light shock load and inner ring rotates.
Answer
Sign in to view the complete answer paper.
Determine the dimensions of cross section of the connecting rod for a diesel engine with the following data: Cylinder bore = 100 mm; Length of connecting rod = 350 mm; Maximum gas pressure = 4 MPa Factor of safety = 6.
Answer
Sign in to view the complete answer paper.
Following data are given for a four-stroke diesel engine: Cylinder bore = 250 mm, Length of stroke = 300 mm, Speed = 600 rpm, Indicated mean effective pressure = 0.6 MPa, Mechanical efficiency = 80%, Maximum gas pressure = 4 MPa, Fuel consumption = 0.25 kg per BP per hr, Higher calorific value of fuel = 44 000 kJ/kg. Assume that 5% of total heat developed in the cylinder is transmitted by the piston. The piston is made of grey cast iron FG 200 (Sut) = 200 N/mm2 and k = 46.6 W/m/oC) and the factor of safety is 5. The temperature difference between the centre and the edge of piston head is 220oC.
a) Calculate the thickness of piston head by strength consideration.
b) Calculate the thickness of piston head by thermal consideration.
c) Which criterion decides the thickness of piston head?
d) State whether ribs required?
e) If so, calculate the number and thickness of the piston ribs.
f) State whether a cup is required in the top of piston head?
g) If so, calculate the radius of the cup.
Answer
Sign in to view the complete answer paper.
Select a suitable wire rope for a wire hoist carrying a load of 80 kN to be lifted from a depth of 100 m. The speed of 10 m/s should be attained in 10 seconds.
Answer
Sign in to view the complete answer paper.
Why Wahl’s factor is to be considered in the design of helical compression or tension springs? Explain.
Answer
Sign in to view the complete answer paper.
A load of 3 kN is dropped axially on a close coiled helical compression spring from a height of 150 mm. The spring has 12 active coils. Take wire diameter as 20 mm, spring index as 6. Determine the deflection and stress induced in the spring. Take G = 8.4 × 104 N/mm2.
Answer
Sign in to view the complete answer paper.
It is required to design a pair of spur gears with 20o full-depth involute teeth based on Lewis equation. The velocity factor is to be used to account for dynamic load. The pinion shaft is connected to a 10 KW, 1440 rpm motor. The starting torque of the motor is 150% of the rated torque. The speed reduction is 4:1. The pinion as well as the gear is made of plain carbon steel 40C8 (S = 600 N/mm2). The factor of safety can be taken as 1.5. Design the gears, specify their dimensions, and suggest suitable surface hardness for the gears.
Answer
Sign in to view the complete answer paper.
A pair of parallel helical gears consists of a 20 teeth pinion meshing with a 100 teeth gear. The pinion rotates at 720 rpm. The normal pressure angle is 20o, while the helix angle is 25o. The face width is 40 mm and the normal module is 4 mm. The pinion as well as the gear is made of steel 40C8 (Sut = 600 N/mm2) and heat treated to a surface hardness of 300 BHN. The service factor and the factor of safety are 1.5 and 2 respectively. Assume that the velocity factor accounts for the dynamic load and calculate the power transmitting capacity of gears.
Answer
Sign in to view the complete answer paper.