PPT: Belts, Chains & Ropes | Theory of Machines (TOM) - Mechanical Engineering PDF Download

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Belt, Rope and Chain Drives
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Belt, Rope and Chain Drives
The belts or ropes are used to transmit power from 
one shaft to another by means of pulleys which 
rotate at the same speed or at different speeds. The 
amount of power transmitted depends upon the 
following factors :
? Velocity of the belt.
? Tension under which the belt is placed on the 
pulleys.
? Arc of contact between the belt and the smaller 
pulley.
Page 3


Belt, Rope and Chain Drives
The belts or ropes are used to transmit power from 
one shaft to another by means of pulleys which 
rotate at the same speed or at different speeds. The 
amount of power transmitted depends upon the 
following factors :
? Velocity of the belt.
? Tension under which the belt is placed on the 
pulleys.
? Arc of contact between the belt and the smaller 
pulley.
Conditions under which the belt is used
? The shafts should be properly in line to insure 
uniform tension across the belt section.
? The pulleys should not be too close together, in 
order that the arc of contact on the smaller pulley 
may be as large as possible.
? The pulleys should not be so far apart as to cause 
the belt to weigh heavily on the shafts, thus 
increasing the friction load on the bearings
Page 4


Belt, Rope and Chain Drives
The belts or ropes are used to transmit power from 
one shaft to another by means of pulleys which 
rotate at the same speed or at different speeds. The 
amount of power transmitted depends upon the 
following factors :
? Velocity of the belt.
? Tension under which the belt is placed on the 
pulleys.
? Arc of contact between the belt and the smaller 
pulley.
Conditions under which the belt is used
? The shafts should be properly in line to insure 
uniform tension across the belt section.
? The pulleys should not be too close together, in 
order that the arc of contact on the smaller pulley 
may be as large as possible.
? The pulleys should not be so far apart as to cause 
the belt to weigh heavily on the shafts, thus 
increasing the friction load on the bearings
? A long belt tends to swing from side to side, causing 
the belt to run out of the pulleys, which in turn 
develops crooked spots in the belt.
? The tight side of the belt should be at the bottom, so 
that whatever sag is present on the loose side will 
increase the arc of contact at the pulleys.
? In order to obtain good results with flat belts, the 
maximum distance between the shafts should not 
exceed 10 metres and the minimum should not be 
less than 3.5 times the diameter of the larger pulley.
Page 5


Belt, Rope and Chain Drives
The belts or ropes are used to transmit power from 
one shaft to another by means of pulleys which 
rotate at the same speed or at different speeds. The 
amount of power transmitted depends upon the 
following factors :
? Velocity of the belt.
? Tension under which the belt is placed on the 
pulleys.
? Arc of contact between the belt and the smaller 
pulley.
Conditions under which the belt is used
? The shafts should be properly in line to insure 
uniform tension across the belt section.
? The pulleys should not be too close together, in 
order that the arc of contact on the smaller pulley 
may be as large as possible.
? The pulleys should not be so far apart as to cause 
the belt to weigh heavily on the shafts, thus 
increasing the friction load on the bearings
? A long belt tends to swing from side to side, causing 
the belt to run out of the pulleys, which in turn 
develops crooked spots in the belt.
? The tight side of the belt should be at the bottom, so 
that whatever sag is present on the loose side will 
increase the arc of contact at the pulleys.
? In order to obtain good results with flat belts, the 
maximum distance between the shafts should not 
exceed 10 metres and the minimum should not be 
less than 3.5 times the diameter of the larger pulley.
Selection of a Belt Drive
? Speed of the driving and driven shafts,
? Speed reduction ratio,
? Power to be transmitted
? Centre distance between the shafts,
? Positive drive requirements
? Shafts layout,
? Space available
? Service conditions.