JNTU B.Tech II THEORY OF MACHINES Previous Question Paper (April - 2018 - R13)

a) Distinguish between the Drag-Crank mechanism and Double–Crank mechanism, with neat sketches. b) A double slider mechanism is used to draw an ellipse with major axis equal to 20 cm and minor axis 15 cm. Set out the mechanism, and draw the locus of the points tracing the required ellipse.

The lengths of various links of a mechanism shown in Figure 1 are as follows: OA = 0.3 m; AB = 1 m; CD = 0.8 m; and AC = CB. For the given configuration, determine the velocity of slider D, if the crank OA rotates at 60 rpm clockwise. Also, find the angular velocity of the link CD. Use the Instantaneous center method.

a) Prove that the maximum length of the arc of contact should be equal to (r + R) tan φ to avoid interference between two involute gears, where r and R are the pitch circle radii of the pinion and gear respectively, and φ is the angle of obliquity. b) A simple Epicyclic gear train is shown in the figure 2. Deduce, from first principles, the expression for velocity ratio of the gear train.

Two mating spur gears have 20 and 40 involute teeth of 4 mm module and 14.5 degree pressure angle. The addendum on each wheel is of a value such that the length of path of contact on either side of the pitch point is of half the maximum possible length. Find the addendum for each gear wheel and the length of the path of contact.

A three - cylinder single - acting reciprocating engine has its cranks set equally at 120 degrees, and it runs at 600 rpm. The torque - crank angle diagram for each cycle is a triangle for the power stroke with a maximum torque of 90 N – m at 60 degrees from the dead center of the corresponding crank. The torque on the return stroke is sensibly zero. Determine the (a) power developed by the engine, (b) coefficient of fluctuation of speed, if the mass of the flywheel is 8 kg, and its radius of gyration is 60 mm, and (c) coefficient of fluctuation of energy.

A leather belt 10 mm thick transmits 45 HP from a pulley of 90 mm diameter running at 300 rpm. The angle of lap is 160 degrees, coefficient of friction is 0.25 and the density of leather is 970 kg/m^3. Calculate the width of the belt required if the maximum stress for the belt material is 240 x 10^3 kg/m^2.

a) What is Centrifugal Tension and how does it affect the belt tensions? Derive an expression for the Centrifugal Tension in a belt drive. b) A square threaded screw of mean diameter 30 mm and pitch of threads 5 mm is used to lift a load of 15 kN by a horizontal force applied at the circumference of the screw. Find the force required if the coefficient of friction between screw and nut is 0.02.

A conical pivot supports a load of 20 kN. The cone angle is 120 degrees, and the intensity of normal pressure is not to exceed 0.3 MPa. The external diameter is 3.5 times the internal diameter. Find the dimensions of the bearing surface. If the coefficient of friction is 0.05, and the speed is 110 rpm, determine the HP absorbed in overcoming friction.

a) Discuss how a single revolving mass is balanced by two masses revolving in different planes. b) Each arm of a Porter governor is 300 mm long and is pivoted on the axis of rotation. Each ball has a mass of 6 kg, and the sleeve weighs 176 N. The radius of rotation of the ball is 200 mm when the governor begins to lift, and 250 mm when the speed is maximum. Determine the maximum and minimum speeds, and the range of speed of the governor.

Draw the profile of a cam to operate a roller follower of 15 mm diameter. The stroke of the follower is offset by 10 mm from the axis of the camshaft. The least radius of the cam is 5 cm, and the lift of follower is to be 4 cm. The out–stroke of the follower occurs with SHM during 150 degrees of cam rotation, followed by a dwell period of 30 degrees of cam rotation. The follower then returns to its original position during 120 degrees of cam rotation with uniform and equal acceleration and retardation, and dwells for the remaining period.