8/13/2019 Assignment 2 Mekanik Mesin S1_20132014

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Assignment Khas Mekanik Mesin

Balancing

1) A shaft carries three pulleys A,B, and C. the pulleys B and C being 1.2m and 2.1m

from A. The pulleys are out of balance to the extent of 0.03, 0.05 and 0.04 kg.m respectivelyand are keyed to the shaft so as to give static balance. Find the relative angular positions of

the radii which define unbalance. If the shaft is supported in bearings 1.8m apart, find the

dynamic loading on each bearing when the shaft rotate at 300rpm.

2) A horizontal shaft supported in bearings 1.2m apart carries 2 masses A and B each of

mass 6kg, placed at distances 0.3m and 0.6m respectively from one of the bearings. Static

balances is obtained by addition of a balance mass of 5kg acting at radius of 200mm, the

positions of the balance mass being midway between A and B. If the radii of the mass centresof A and B are 175mm and 225mm respectively, find the relative angular positions of the 3

masses and also the magnitude of the unbalanced coupled acting on bearingnwhen the shaft

rotates at 100rpm.

3) The out-of-balance of a machine rotor is equivalent to 5kg at 10mm radius in one

plane A, together with an equal mass at 15mm radius in a second plane B. AB=375mm and

the two radii are at 120. Find the mass required in a third plane C at a radius of 125mm and

its angular positions with respect to the given radii so that there is no resultant out-of-balanceforce. Find also the positions of C along the axis for the residual couple to be a minimum and

the value of this couple when the speed is 500rpm.

4) A shaft rotating at 120rpm is supported at bearing A and B that is 1.8m apart. Two

unbalanced rotating mass C and D of 7.5kg and 10kg at radii 75mm and 50mm are situated

between A and B at distance 0.6m and 0.9m from A. The angle between C and D is 60. Find

the magnitude, directions and senses of the forces of the shaft on the bearings due to the

combined action of the dynamical forces and gravity when the 7.5kg mass is vertical and

above the shaft and the 10kg mass is on the right of the 7.5kg mass when view from B to A.

Show the result (direction of force/mass location) in an end view looking from A to B.

8/13/2019 Assignment 2 Mekanik Mesin S1_20132014

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Friction

1) A turnbuckle with right and left hand threads is used to couple two railway coaches. It

has single threads with pitch of 15 mm on a mean diameter of 60 mm. Taking the coefficient

of friction as 0.2, find the work done in drawing the coaches together, a distance of 20.8 cm

(a) against a steady load of 2500 N (b) Efficency.

2) A power shaft running at 180rpm drives a countershaft through a single-plate friction

clutch of internal and external radii 75mm and 150mm respectively. The countershaft has a

moment of inertia 8.4kg.m2. If the time taken for the countershaft to attain fullspeed from rest

is 6s, determined the axial spring force in the clutch, and also work dissipated due to clutch

slip. Assume uniform wear and =0.3

3) A cone clutch is required to transmit 30kW at 1200 rpm. The mean diameter of

bearing surface is 250mm and the cone angle is 25. Assuming =0.3 and a normal pressure

of 140kN/m2, determine the axial width of the conical bearing surface and the axial load

required.

4) A multi-disc friction clutch has to be designed to transmit 75kW from an engine

running at 2000rpm. Assuming that the maximum pressure is 150kN/m2

and the inner and theouter diameter of the lining are respectively 100mm and 150mm. Determine the necessary

number of plates. Take =0.25.