Subject: Fundamental of Mechanical Engineering
Ch.1Power Transmission and Safety
Q 1. What is power transmission?
Ans:
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To operate machines, velocity and power of various mechanical machines, electric
motors and I.C. engines are being transmitted.
Velocity and power are transmitted from one shaft of the machine to another shaft of
the machine.
For this purpose belt, rope and chain drives are used
Positive drive such as gears and clutch are also used.
Q 2. Explain importance of power transmission:
Ans:
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As we know, electric motors are used in industrial to run the machines.
Velocity and power of electric motors are transmitted to operate various machine
tools such as lathe, shaping machine, drill machine etc.
Q 3. Explain types of belts:
Ans:
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Flat belt
V-belt
Q 4. Explain types of flat belt drive
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Open belt drive
Cross belt drive
Quarter turn belt dri
Belt drive with idler pulley
Compound belt drive
Cone pully drive
Fast and loose
1) Open belt drive:
When two shaft are running in the same direction and parallel to echother then this drive is
used.
dL - Diameter of the larger pulley
dS – Diameter of the smaller pulley
αL- Angle of wrap of the larger pulley
αS – Angle of wrap of the smaller pulley
C- Center distance between the two pulleys
Basic Formulae
ο
αL = 180 + 2β
ο
αS = 180 - 2β
Where angle β is
(2) Cross belt drive:
Fig indicate cross belt drive. This drive is also called twist belt drive this drive is used when
two parallel shaft are running in opposite direction.
d - Diameter of the larger pulley
L
d – Diameter of the smaller pulley
S
α - Angle of wrap of the larger pulley
L
α – Angle of wrap of the smaller pulley
S
C- Center distance between the two pulleys
Basic Formulae
α
ο
α = 180 + 2β
L=
S
Where angle β is,
Length of cross belt
Q 5 What are the advantages of a belt drive?
Ans:
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The advantages of a belt drive are that, it can absorb a good amount of shock and
vibration.
It can take care of some degree of misalignment between the driven and the driver
machines and long distance power transmission, in comparison to other transmission
systems, is possible.
Q 6. Why the slack side of the belt of a horizontal belt drive is preferable to
place on the top side?
Ans:
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The slack side of the belt is preferably placed on the top side because, the slack side
of the belt, due to its self-weight, will sag.
For this reason the angle of contact between the belt and the pulleys will increase.
However, the tight side will not sag to that extent.
Hence, the net effect will be an increase in the angle of contact or angle of wrap.
Thus, due to the increase in angle of contact, the power transmission capacity of the
drive system will increase.
Q 7. Which one should be the governing pulley to calculate tension ratio?
Ans.
 The pulley, driven or driver, for which the product, μα of equation for belt tension is
the least, should be considered to determine the tension ratio.