JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS - II Previous Question Paper (May/June - 2019 - R16)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
PART - A
List the assumptions made in Reynolds’s equation of hydrodynamic lubrication.
Answer
- The lubricant is a Newtonian fluid.
- The flow is laminar and steady.
- The lubricant is incompressible.
- The pressure is constant across the film thickness.
- The surfaces are smooth and the film thickness is small compared to the dimensions of the bearing.
The Saybolt kinematic viscosity of oil corresponds to 60 seconds at 90°C. What is the corresponding absolute viscosity in centipoises?
Answer
The kinematic viscosity in centistokes (ν) is calculated using the formula: ν = 0.226t - 195/t, where t is 60 seconds. Substituting the value: ν = 0.226(60) - 195/60 = 13.56 - 3.25 = 10.31 cSt. Assuming the specific gravity of oil is approximately 0.9, the absolute viscosity (η) = ν × ρ = 10.31 × 0.9 = 9.279 centipoises.
Define rating life of bearing.
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A taper roller bearing has a dynamic load capacity of 25 kN. Calculate the equivalent radial load that the bearing can carry if the rated bearing life (L10) is 150 million revolutions.
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Name the materials used for engine piston.
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What is whipping stress? Explain the method to calculate the whipping stress.
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Explain Nipping in automobile suspension springs.
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Enumerate the steps involved in the design of wire ropes.
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Why is the pinion weaker than the gear made of same material?
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An 18-tooth pinion with a 3 mm module rotates 2400 rpm and drives a gear at 1200 rpm. What are the number of teeth in the gear, the center distance, and the pitch diameters of the gears?
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PART - B
With a neat sketch explain the radial pressure distribution in a journal bearing.
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An 80 mm diameter shaft is supported by a full-journal bearing of 120 mm length with a radial clearance of 0.05 mm. It is lubricated by SAE 10 oil at 70°C. The shaft rotates 1200 rpm and is under a radial load of 500 N. Apply Petroff’s equation to determine the bearing coefficient of friction and the friction torque and power loss.
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A 5 kN load is applied to a 100 mm diameter shaft rotating at 2000 rpm. A journal bearing is used to carry the load. The journal bearing with a diameter to length ratio of 0.25 is lubricated with an SAE 40 oil with an inlet temperature of 40°C. Determine the minimum oil film thickness bearing coefficient of friction and its angular location, the maximum pressure within the oil film and its angular location, and the side flow.
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A rolling contact bearing is subjected to the following work cycle: Radial load of 6000 N at 150 rpm for 25% of the time; Radial load of 7500 N at 600 rpm for 20% of the time; Radial load of 3000 N at 300 rpm for 55% of the time. The inner ring rotates and loads are steady. Select a bearing for an expected average life of 2500 hours. Also, find out the reliability with which the life could be expected.
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Why are ball and roller bearings called ‘antifriction’ bearings?
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Select a ball bearing for an industrial machine press fit onto a shaft and intended for continuous one-shift (8-hour day) operation at 1800 rpm. Radial and thrust loads are 1.2 and 1.5 kN, respectively, with light-to-moderate impact.
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Design a cast iron piston for a single acting four stroke engine for the following data: Cylinder bore = 100 mm; Stroke = 125 mm; Maximum gas pressure = 5 MPa; Indicated mean effective pressure = 0.75 MPa; Fuel consumption = 0.15 kg per brake power per hour; Higher calorific value of fuel = 42 000 kJ/kg; Speed = 2000 rpm. Any other data required for the design may be assumed.
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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; R.P.M. = 1500 with possible over speed of 2500; Compression ratio = 4: 1; Maximum explosion pressure = 2.5 MPa.
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Design a helical extension spring to handle a dynamic load that varies from 275 N to 325 N over 10-mm working deflection. Use chrome silicon wire and standard hooks. The forcing frequency is 800 rpm. Infinite life is desired. Minimize the package size. Choose appropriate safety factors against fatigue, yielding, and surging.
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Design a V-belt drive to connect a 10 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.
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The following data is given for a pair of spur gears with 20° full-depth involute teeth: Number of teeth on pinion = 24; Number of teeth on gear = 56; module = 3 mm; Speed of pinion = 1200 rpm; service factor = 1.5; Face width = 30 mm. Both gears are made of steel with an ultimate tensile strength of 600 MPa. Using the velocity factor to account for the dynamic load, calculate beam strength, velocity factor and rated power that the gears can transmit without bending failure.
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Compare the contact between mating teeth of spur and helical gears.
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A pair of parallel helical gears consists of an 18 teeth pinion meshing with a 45 teeth gear. 7.5 kW power at 2000 rpm is supplied to the pinion through its shaft. The normal module is 6 mm, while the normal pressure angle is 20°. The helix angle is 23°. Determine the tangential, radial and axial components of the resultant tooth force between the meshing teeth.
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