JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III DESIGN OF MACHINE MEMBERS II Previous Question Paper (February - 2023 - R16)
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.
PART - A
What is journal bearing? List any two types of journal bearings depending upon the nature of contact.
Answer
A journal bearing is a type of sliding contact bearing in which the rotating machine element, known as the journal, is supported by and slides over a stationary member called the bearing or bush, typically separated by a thin film of lubricant. Depending on the nature of contact, the two types are full journal bearings, where the contact angle of the bearing is 360 degrees, and partial journal bearings, where the contact angle is less than 360 degrees.
A journal bearing has a shaft diameter of 40 mm and a length of 40 mm. The shaft is rotating at 20 rad/sec and viscosity of lubricant is 20 MPa-s. The clearance is 0.020 mm. What is the loss of the torque due to viscosity of the lubricant?
Answer
To calculate the frictional torque loss in a journal bearing, we use the Petroff's equation for viscous friction. Given: shaft diameter d = 0.04 m (radius r = 0.02 m), length l = 0.04 m, angular velocity ω = 20 rad/s, dynamic viscosity μ = 20 MPa-s = 0.02 N-s/m2, and radial clearance c = 0.020 mm = 0.00002 m.
The shear stress τ is given by:
The frictional force F is:
The frictional torque T is:
Substituting the values:
The loss of torque due to the viscosity of the lubricant is 2.011 N-m.
What are rolling contact bearings?
Answer
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Write short note on classifications antifriction bearings.
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What is the function of gudgeon pin?
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Why are the connecting rods made of I – Section?
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What are the advantages of fabric rubber belts?
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Explain the designation of V-belt with the help of examples.
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Define (i) Load concentration factor and (ii) Dynamic load factor with respect to spur gears.
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Why are crossed helical gears not used for high power transmission?
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PART - B
In journal bearing distinguish between bearing characteristics number and bearing modulus.
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A journal bearing of 75 mm long and 150 mm diameter has diametral clearance of 0.25 mm. Journal rotates at 3000 rpm. Compare the power loss and friction torque for SAE 10, SAE20 and SAE60 grade oils. Make suitable assumptions 5 kN radial load is acting on the bearing.
Answer
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What procedure would you follow while designing a journal bearing? Explain.
Answer
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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.
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Give the relative advantages and disadvantages of ball and roller bearings as compared to journal bearings.
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Determine the type and size of ball bearing for a 75 mm shaft. The shaft speed is 325 rpm, the radial load is 9 kN, with very light shocks and the axial load is 3.5 kN. The installation is a temporary one, to serve not over 1 year with 8 hr service per day. The bearing is to be placed 0.9 m from one end of the shaft.
Answer
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How do you express the life of a bearing? What is an average or median life? Explain.
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Define the following terms as applied to rolling contact bearings: (i) Basic static load rating (ii) Static equivalent load (iii) Basic dynamic load rating.
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Discuss the design of connecting rod for an internal combustion engine.
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Explain the design of a center crankshaft when the crank is at the TDC position, and subjected to maximum bending moment and no torsional moment.
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Design a suitable connecting rod for a petrol engine for the following data: Diameter of the piston = 100 mm; Weight of reciprocating parts per cylinder = 20N; Connecting rod length = 300 mm; Compression ratio = 7:1; Maximum explosion pressure = 3 N / mm2; Stroke = 140 mm; Engine speed = 2000 rpm.
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What are advantages of wire rope drive over belt drive?
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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.
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A compression spring of spring constant K is cut into two springs having equal number of turns and the two springs are then used in parallel. What is the resulting spring constant of the combination? How does the load carrying capacity of the resulting combination compare with that of the original spring?
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Explain, with the help of neat sketches, the types of various flat belt drives.
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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.
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Derive the expression to estimate beam strength in bevel gears.
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Describe the interference phenomenon in involute gears. Also, state the conditions to avoid interference.
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A pair of parallel helical gear consists of an 18 teeth pinion meshing with a 45 teeth gear. The normal module is 3 mm. The helix angle is 23o while the normal pressure angle is 20o. Calculate: i) the transverse module, ii) transverse pressure angle and axial pitch.
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