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Registration No: Total Number of Pages: 02 B.Tech. PCMF4203 3rd Semester Back Examination 2017-18 THEORY OF MACHINES BRANCH : MANUTECH, PE Time: 3 Hours Max Marks: 70 Q.CODE: B893 Answer Question No.1 which is compulsory and any five from the rest. The figures in the right hand margin indicate marks. Q1 a) b) c) d) e) f) g) h) i) j) Answer the following questions : What do you understand by a kinematic link? Differentiate between lower pair and higher pair with suitable examples. Explain Grashof’s law for a four bar mechanism with proper sketch. A screw will be self locking if ____________. What is the difference between the clutch and the brake? What are the advantages of epicyclic gear train? What is interference and undercutting related to gears? Why a roller follower is preferred to that of a knife-edged follower? What is the function of a governor? How does it differ from that of a flywheel? Explain hunting related to governors. (2 x 10) Q2 a) b) Sketch and explain the various inversions of a slider crank chain. The whitworth quick return motion mechanism has the driving crank 150 mm long. The distance between fixed centres is 100 mm. The line of stroke of the ram passes through the centre of rotation of the slotted lever whose free end is connected to the ram by a connecting link. Find the ratio of time of cutting to time of return. (5) (5) Q3 a) A vertical two start square threaded screw of a 100 mm mean diameter and 20 mm pitch supports a vertical load of 18 kN. The axial thrust on the screw is taken by a collar bearing of 250 mm outside diameter and 100 mm inside diameter. Find the force required at the end of a lever which is 400 mm long in order to lift and lower the load. The coefficient of friction for the vertical screw and nut is 0.15 and that for collar bearing is 0.20. State and prove the law of gearing. Show that involute profile satisfies the conditions for correct gearing. (5) A plate clutch has three discs on the driving shaft and two discs on the driven shaft, providing four pairs of contact surfaces. The outside diameter of the contact surface is 240 mm and inside diameter 120 mm. Assuming uniform pressure and = 0.3; find the total spring load pressing the plates together to transmit 25 kW at 1575 r.p.m. If there are 6 springs each of stiffness 13 kN/m and each of the contact surfaces has worn away by 1.25 mm, find the maximum power that can be transmitted, assuming uniform wear. (10) A compound train consists of six gears. The number of teeth on gears are as follows : Gear: A B C D E F No. of teeth: 60 40 50 25 30 24 (5) b) Q4 Q5 a) (5)

b) The gears B and C are on one shaft while the gears D and E are on another shaft. The gear A drives gear B, gear C drives gear D and gear E drives gear F. If the gear A transmits 1.5 kW at 100 r.p.m. and the gear train has an efficiency of 80 per cent, find the torque on gear F. Four masses A, B, C and D revolve at equal radii and are equally spaced along a shaft. The mass B is 7 kg and the radii of C and D make angles of 90˚ and 240˚ respectively with the radius of B. Find the magnitude of the masses A, C and D and the angular position of A so that the system may be completely balanced. (5) Q6 The upper arms of a Porter governor has lengths 350 mm and are pivoted on the axis of rotation. The lower arms has lengths 300 mm and are attached to the sleeve at a distance of 40 mm from the axis. Each ball has a mass of 4 kg and mass on the sleeve is 45 kg. Determine the equilibrium speed for a radius of rotation of 200 mm and find also the effort and power of the governor for 1 percent speed change. (10) Q7 A cam drives a flat reciprocating follower in the following manner: During first 120˚rotation of the cam, follower moves outwards through a distance of 20 mm with simple harmonic motion. The follower dwells during next 30˚ of cam rotation. During next 120˚ of cam rotation, the follower moves inwards with simple harmonic motion. The follower dwells for the next 90˚ of cam rotation. The minimum radius of the cam is 25 mm. Draw the profile of the cam. (10) Q8 Write short answer on any TWO : Hunting Grubler’s criteria for determining degree of freedom for mechanisms ‘Interference’ related to gears Hammer Blow a) b) c) d) (5 x 2)

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