Rr321401-principles-of-machine-design

Set No. 1

Code No: RR321401

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Compare the weights of equal lengths of hollow shaft and solid shaft to transmit a given torque for the same maximum shear stress. The material for both the shafts is same and inside diameter is 2/3 of outside diameter in case of hollow shaft.[16] 2. Determine the diameter of hollow shaft having inside diameter 0.5 times the out side diameter. The permissible shear stress is limited to 200 MPa. The shaft carries a 900 mm diameter cast iron pulley. This pulley is driven by another pulley mounted on the shaft placed below it. The belt ends are parallel and vertical. The ratio of tensions in the belt is 3. The pulley on the hollow shaft weighs 800 N and overhangs the nearest bearing by 250 mm. The pulley is to transmit 35 kW at 400 rpm. [16] 3. (a) What is the importance of the dimensionless groups in the design of journal bearings. (b) A full-length bearing operates with the following data Length of bearing = 150 mm Dia of bearing = 100mm Radial load on bearing = 25kN Speed of journal = 250 rpm Radial clearance = 0.045 mm It is desired to limit minimum oil film thickness to 0.025mm. Determine a suitable value for the viscosity of the lubricant and the power loss due to friction. [4+12] 4. Design and make a neat dimensional sketch of a muff coupling which is used to connect two steel shafts transmitting 40kW at 350 rpm. The material for the shaft and key is plain carbon steel for which allowable shear and crushing stress may be taken as 40N/mm2 respectively. The material for the cast iron for which the allowable shear stress may be assumed as 15N/mm2 . Take standard proportions. [16] 5. A carbon steel rod of circular cross-section having σu =600MN/m2 , σy =450 MN/m2 , ′ σe = 300 MN/m2 is subjected to a bending moment which varies between 300 to 500 Nm and axial load which varies between 5 to 10 kN. Assuming that the bending moment and axial load are in phase determine the diameter of the rod to have a factor of safety of 2. [16] 6. Determine the dimensions of an I-Section connecting rod for a petrol engine from the following data: 1 of 2

Set No. 1

Code No: RR321401

Diameter of the piston = 110 mm; Mass of the reciprocating parts = 2 kg; Length of the connecting rod from center to center = 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 N/mm2 .

[16]

7. A 50 kW, 1200 rpm, high torque squirrel-cage motor is used to drive a punch press. The speed of the punch press flywheel is 300 rpm. If the center distance is 2.5 m, select a suitable leather belt. [16] 8. Design a pair of spur gears to drive a lobe-blower from a 120 kW motor running at 2880 rpm. With a reduction ratio of 1.6. The pitch diameter of the pinion is not to be more than 80 mm. Drive is an enclosed one with proper lubrication. Life to be indefinite. Light shock loads are likely. [16] Name Material (Steel) Design compressive Design bending stress (N/mm2 ) stress (N/mm2 ) Pinion CI 35 600 550 Gear CI 25 600 400 ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR321401

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. A shaft is subjected to a twisting moment of 5kN-m and a bending moment of 2kN-m. If the material has Sy = 330 MPa and F.S= 2, find the diameter of shaft using (a) Maximum shear stress theory (b) Maximum energy of distortion theory

[8+8]

2. A hoisting drum 500 mm in diameter is keyed to a shaft which is supported in two bearings and driven through a 12:1 reduction gearing by an electric motor. Determine the horse power of the driving motor if the maximum load of 8000 N is hoisted at a speed of 50m/min and the efficiency of the drive be 80%. Also determine the torque on the drum shaft and the speed of the motor. Determine the diameter of the shaft made of machinery steel, the working stresses for which are 115 MPa in tension and 56MPa in shear. The drive gear, whose diameter is 450mm is mounted at the end of the shaft such that it overhangs the nearest bearings by 150mm. The combined shock and fatigue factors for bending and torsion may be taken as 2 and 1.5 respectively. [5+5+6=16] 3. (a) What are desirable properties of a bearing material? (b) A full journal bearing of 50 mm diameter and 100 mm long has a Bearing pressure of 1.4 N/mm2 . The speed of the journal is 900 rpm and the ratio of journal diameter to the diametral clearance is 1000.The bearing is lubricated with oil whose absolute viscosity at the operating temperature of 75o C may be taken as 0.011 kg/m.s. The room temperature is 35o C. Find: i. The amount of artificial cooling required, and ii. The mass of the lubricating oil required if the difference between the outlet and inlet temperature of the oil is 10 o C. Take specific heat of the oil as 1850 J/kg/o C. [5+5+6] 4. The split muff coupling is to be designed to transmit 67.5 kW at 180 rpm. Determine the diameter of the solid shaft if the permissible shear in the shaft material is limited to 42 MPa. Assuming that the two halves of the coupling are connected by 8 bolts, determine the diameter of each clamping bolt if the permissible tensile stress intensity for the bolt material is limited to 70 MPa. The coefficient of friction between the shaft and muff may be taken as 0.3. [8+8] 5. A simply supported beam has a concentrated load at the center which fluctuates from a value of P to 4 P. The span of the beam is 500 mm and its cross-section is 1 of 2

Set No. 2

Code No: RR321401

circular with a diameter of 60 mm. Taking for the beam material an ultimate stress of 700 MPa, a yield stress of 500 MPa, endurance limit of 330 MPa for reversed bending, and a factor of safety of 1.3, calculate the maximum value of P. Take a size factor of 0.85 and a surface finish factor of 0.9. [16] 6. The following particulars relate to a slow speed oil engine working on four stroke cycle: Indicate power = 15 kW RPM = 300 Maximum explosion pressure = 2.1 MN/m2 Mean effective pressure = 0.56 MN/m2 Design: (a) The suitable trunk piston and piston rings (b) The piston pin and give a neat sketch of the piston assemble, incorporating all necessary details, clearly indicating the materials used for each part. [8+8] 7. A 50 kW, 1200 rpm, high torque squirrel-cage motor is used to drive a punch press. The speed of the punch press flywheel is 300 rpm. If the center distance is 2.5 m, select a suitable leather belt. [16] 8. A spur gear drive is used to drive a camshaft by the crankshaft with a speed reduction of 2 in a 5 kW engine. The center distance is to be not more than 160 mm. Design the drive for 10,000 hours. Crankshaft speed is 1500 rpm. Assume pinion, gear are C 15 steel and cast iron grade 30, pressure angle 200 , Design compressive stress for pinion, gear are 772 N/mm2 , 350 N/mm2 , design bending stresses for pinion, gear are 85 N/mm2 , 55 N/mm2 . [16] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: RR321401

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What are the main alloying elements in alloy steels? Why are these alloying elements added? (b) What is the significance of theories of failure? Discuss the most commonly used theories. [8+8] 2. A rotating shaft is subjected to a steady bending moment of 1.5 kN-m and a suddenly applied torque of 1 kN-m with minor shocks. Assuming allowable shear stress for shaft material to be 55 N/mm2 , determine the diameter of the shaft.[16] 3. (a) Determine the minimum value of the basic dynamic load rating for selecting ball bearings to give 5000 hrs of operations with not more than 10 percent failures. The radial load is 1800 N during 90 percent of the time and 7200 N during the remaining 10 percent. The shaft is to rotate at 150 rpm. (b) 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 3000hrs. [8+8] 4. Design a split muff coupling to transmit 10 kW at 1000 rpm. The muff is made of FG200 CI and the shaft and the key are made of C20 steel. The coefficient of friction between the shaft and coupling is 0.25. [16] 5. A pulley is keyed to a shaft midway between two bearings. The shaft is made of cold drawn steel for which the ultimate strength is 550 MPa and the yield strength is 400 MPa. The bending moment at the pulley varies from - 150 N-m to + 400 N-m as the torque on the shaft varies from - 50 N-m to + 150 N-m. Obtain the diameter of the shaft for an indefinite life. The stress concentration factors for the keyway at the pulley in bending and in torsion are 1.6 and 1.3 respectively. Take the following values. Factor of safety = 1.5 Load correction factors = 1.0 in bending, and 0.6 in torsion Size effect factor = 0.85 Surface effect factor = 0.88 [16] 6. Design a connecting rod for a petrol engine from the following data: Diameter of the piston = 120 mm Weight of the reciprocating part = 2.0 kg Length of the connecting rod = 300 mm Stroke length = 140 mm 1 of 2

Set No. 3

Code No: RR321401 Speed Maximum explosion pressure

= 2000 rpm = 2.25 N/mm2

7. Select suitable V-belt for the following data. Power to be transmitted = 50 kW Speed of the driving pulley = 960 rpm Velocity ratio desired = 3 Specify all the details

[16]

[16]

8. Design a pair of spur gears to transmit 20 hp at a pinion speed of 1500 rpm. Transmission ratio is to be 3. [16] Name

Material (Steel)

Design compressive Design bending stress (N/mm2 ) stress (N/mm2 ) Pinion 15 N I 2 Cr l M0 15 C 45 950 320 Gear C 45 500 140 ⋆⋆⋆⋆⋆

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Set No. 4

Code No: RR321401

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF MACHINE DESIGN (Mechatronics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Differentiate between preferred numbers and rounding of numbers. (b) What you meant by design stress. How the design stress is determined for ductile and brittle materials. [8+8] 2. A propeller shaft transmits a twisting moment of 90 kN-m and a simultaneous bending moment of kN-m and an axial thrust of 125 kN. If the permissible stresses in tension and shear are 105 N/mm2 and 75 N/mm2 respectively, determine the outer and inner diameters of the hollow shaft for which the outer diameter is 75 percent more than the inner diameter. A machinery shaft supported on bearings 3 m apart is to transmit 120 kW at 250 rpm while subjected to a bending load of 6 kN acting at a distance of 1.2 m from the left hand bearing. The material has an allowable shear stress of 45 MPa and a bending stress of 85 MPa. Determine the required diameter of the shaft if the transverse load is assumed steady while the torsional load is considered to be applied suddenly. [16] 3. (a) Discuss the stable and unstable lubrication with the help of chart. (b) A 3kN load is supported by a journal bearing of 75mm dia and 75mm long, diametal clearance 0.05 mm and bearing is lubricated by an oil of 0.0207 Pa-s viscosity at operating temperature. Determine the maximum speed of rotation of bearing when it is capable of dissipating 80 watts by heat transfer. [4+12] 4. A flanged protective type coupling is required to transmit 50 kW at 2000 rpm. Find (a) Shaft diameter if the driving shaft is hollow with d1 /d0 = 0.6 and driven shaft is a solid shaft. Takeτ = 100 MPa. (b) Diameter of bolts, if the coupling uses four bolts. Take σc = σt =70 MPa and τ = 25 MPa. Assume pitch circle diameter as about 3 times the outside diameter of the hollow shaft. (c) Thickness of the flange and diameter of the hub. Assume σc =100 MPa and τ = 125 MPa. (d) Make a neat free hand sketch of the assembled coupling showing a longitudinal sectional elevation with the main dimensions. The other dimensions assumed suitably. [4+4+4+4] ′

5. A hot rolled steel shaft having σu =600 MN/m2 , σy =450 MN/m2 , σe =300 MN/m2 is subjected to a variable bending moment which varies between + 300 to -200 Nm 1 of 2

Set No. 4

Code No: RR321401

and a variable torque which varies between 250 to - 150 Nm. Neglecting any stressconcentration factor, determine the diameter of the shaft to have a factor of safety of 2. [16] 6. Design a suitable connecting rod for a car with the following data: Piston diameter = 68 mm Stroke length = 80 mm Length of the connecting rod = 160 mm Maximum explosion pressure = 3.5 N/mm2 Weight of the reciprocating part = 2.5 kg Speed = 4000 rpm Compression ratio = 8:1

[16]

7. A 50 kW, 1200 rpm, high torque squirrel-cage motor is used to drive a punch press. The speed of the punch press flywheel is 300 rpm. If the center distance is 2.5 m, select a suitable leather belt. [16] 8. A pair of 200 full depth spur gears are required to transmit 22.5 kW. The speed of the pinion is 3000 rpm and the gear ratio of the drive is 10. The pinion of steel with a Brinell number of 250 and the gear is made of ordinary cast iron. The number of teeth of the pinion should be between 15 and 24. The diameter of the pinion should be approximately 75 mm. Design the spur gear drive. [16] ⋆⋆⋆⋆⋆

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