Page 164 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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Objective Questions
1 The variable speed ratio in a belt drive is because ______.
(a) the contact angles of the driving sheave and driven sheave are different
(b) of belt slippage
(c) the coefficient of friction is unstable
(d) of theelastic creepofthe belt

2 In V-belt drive design, the purpose of limiting the minimum diameter of small sheave
is ______.
(a) to limit bending stress
(b) to make structure compact
(c) to ensure enough friction on the contact surface between the belt and sheave
(d) to limit contact angle on the small sheave

3 The difference between tensions on the tight side and slack side of a belt drive is
−1
3000 N. If the belt speed is 15 m s , the transmitted power is ______ kW.
(a) 90
(b) 22.5
(c) 100
(d) 45

4 The selection of a belt type is according to ______.
(a) the diameter of driving sheave
(b) the rotational speed of a belt drive
(c) the calculated power and the rotational speed of the driving sheave
(d) the transmitted power

5 The reason of elastic creep in a belt drive is because ________.
(a) thebeltisnot absolutely flexible
(b) the coefficient of friction is small
(c) the centrifugal force appears
(d) of the difference between tight side tension and slack side tension

Calculation Questions

1 A flat belt transmits power between two 600 mm diameter pulleys. The coefficient
of friction between the belt and pulley is 0.3. The force acting on the sheave shaft
should not exceed 1200 N. Find the limiting values of the tight side tension F and
1
slack side tension F . Disregard service factors.
2
2 For a flat belt drive with diameters of D = 125 mm and D = 400 mm, if the input
1 2
shaft rotates at 1440 rpm, calculate
(1) the rotational speed of the driven shaft if no elastic creep is considered.
(2) the rotational speed of the driven shaft if a slip ratio is 2%.
(3) how to compensate for the elastic creep.