FUNDAMENTAL UNDERSTANDING FUNDAMENTAL UNDERSTANDING OF OF
PULLEYS AND BELTDRIVESPULLEYS AND BELTDRIVES
ELEMENTS OF TECHNOLOGYELEMENTS OF TECHNOLOGY
WHAT ARE BELT DRIVESWHAT ARE BELT DRIVES A belt drive is a method of transferring rotary motion between A belt drive is a method of transferring rotary motion between
two shafts.two shafts.
A belt drive includes one pulley on each shaft and one or more A belt drive includes one pulley on each shaft and one or more
continuous belts over the two pulleys.continuous belts over the two pulleys.
The motion of the driving pulley is, generally, transferred to the The motion of the driving pulley is, generally, transferred to the
driven pulley via the friction between the belt and the pulley.driven pulley via the friction between the belt and the pulley.
Generally belt drives are friction drives.Generally belt drives are friction drives.
A Belt is a looped strip of flexible material, used to A Belt is a looped strip of flexible material, used to
mechanically link two or more rotating shafts.mechanically link two or more rotating shafts.
A pulley is a wheel with a groove between two flanges around A pulley is a wheel with a groove between two flanges around
its circumference. Pulleys are keyed to the shafts.its circumference. Pulleys are keyed to the shafts.
TYPES OF BELTSTYPES OF BELTSThere are 4 types belts used in belt drives they are as follows:
Flat beltsshaft distance 5 to 10 meters, low power, high speed
Round belts smaller initial tension, absence of vibration and noise, high power, shaft distance > 5 meters
V belts shaft distance < 2 meters, high power, moderate speed
Timing Belts positive drives, precise, reliable
ROUND BELTROUND BELT Round belts are a circular cross section belt Round belts are a circular cross section belt
designed to run in a pulley with a circular (or designed to run in a pulley with a circular (or
near circular) groove.near circular) groove.
The circular belt or rope is mostly used in the The circular belt or rope is mostly used in the
factories where a great amount of power is to factories where a great amount of power is to
be transmitted from one pulley to another, be transmitted from one pulley to another,
when the two pulleys are more than 5 meters when the two pulleys are more than 5 meters
apart.apart.
FLAT BELTSFLAT BELTS Flat belts find their widest application Flat belts find their widest application
where high-speed motion, rather than where high-speed motion, rather than
power, is the main concern.power, is the main concern.
Flat belts are made from leather, woven Flat belts are made from leather, woven
cotton, rubber, balata (wood gum).cotton, rubber, balata (wood gum).
‘‘V’ BELTSV’ BELTS The strength of these belts is obtained by The strength of these belts is obtained by
reinforcements with fibers like steel, reinforcements with fibers like steel,
polyester.polyester.
V-belts are far superior to flat belts at V-belts are far superior to flat belts at
small center distances and high reduction small center distances and high reduction
ratios. ratios.
Require larger pulleys than flat belts Require larger pulleys than flat belts
because of their greater thickness. because of their greater thickness.
The The "V""V" shape of the belt tracks in a shape of the belt tracks in a
mating groove (or sheave) in the pulley, mating groove (or sheave) in the pulley,
with the result that the belt cannot slip off.with the result that the belt cannot slip off.
TIMING BELTSTIMING BELTS Also known as Also known as ToothedToothed, , NotchNotch or or CogCog
belts are a belts are a positivepositive transfer belt and can transfer belt and can
track relative movement. track relative movement.
These belts have teeth that fit into a These belts have teeth that fit into a
matching toothed pulley .matching toothed pulley .
They are often used to replace chains or They are often used to replace chains or
gears, reducing noise and avoiding the gears, reducing noise and avoiding the
lubrication bath or oiling system lubrication bath or oiling system
requirement. requirement.
Requires the least tension of all belt drives Requires the least tension of all belt drives
and are among the most efficient. and are among the most efficient.
Types of Belt drives based on the arrangement are as follows
• OPEN BELT DRIVES
• CROSSED OR TWIST BELT DRIVES
• BELT DRIVE WITH IDLER PULLEYS
• COMPOUND BELT DRIVE
TYPES OF BELT DRIVES TYPES OF BELT DRIVES BASED ON BASED ON
ARRANGEMENTARRANGEMENT
OPEN BELT DRIVEOPEN BELT DRIVE The Open belt drive is arranged with The Open belt drive is arranged with
shafts arranged parallel and rotating in shafts arranged parallel and rotating in
the same direction.the same direction.
The driver pulls the belt from one side The driver pulls the belt from one side
and delivers it to the other side thus the and delivers it to the other side thus the
tension in the one side belt will be more tension in the one side belt will be more
than that in the other side belt.than that in the other side belt.
X
d1 d2
21
1dr
22
2dr
xx
dd rr )22(2
2
)( 2121
Length of the open belt=Length of the open belt=
CROSSED OR TWIST BELT DRIVECROSSED OR TWIST BELT DRIVE The crossed or twist belt drive is The crossed or twist belt drive is
used with shafts arranged parallel used with shafts arranged parallel and rotating in the opposite and rotating in the opposite directions.directions.
The tension in the tight side will be The tension in the tight side will be more than the slack side. The more than the slack side. The point where the belts rubs against point where the belts rubs against each other and there will be each other and there will be excessive wear and tear.excessive wear and tear.
To avoid this the shafts should be To avoid this the shafts should be placed at a maximum distance of placed at a maximum distance of 20b where b is the width of the 20b where b is the width of the belt and the speed should be less belt and the speed should be less than 15 m/s.than 15 m/s.
X
21
1dr
22
2dr
Length of the cross belt=x
rrx
dd )22(2
2
)( 2121
Velocity of Belt (V)=60
dNWhere ( d=diameter of pulley (mts), N=Revolutions per minute (RPM), V=velocity of belt in
mts/sec )Effective Tension in the belt (T) = (T1-T2)
Power (P) = T x V =60
)()( 21 dNTT
Power (P) =45000
dNTHere ( d=diameter in meters, N=Speed in RPM, P=power in HP (Horse Power), T= Tension in the belt in Kgs )
Power (P) =60
11NdT Here ( d1=diameter in meters, N1=Speed in RPM, P1=power in Watts, T= Tension in the belt N )
COMPOUND BELT DRIVECOMPOUND BELT DRIVE
A compound belt drive is used A compound belt drive is used
when power is transmitted from when power is transmitted from
one shaft to another through a one shaft to another through a
number of pulleys.number of pulleys.
The belts are connected in such The belts are connected in such
a way that the driver moving one a way that the driver moving one
system of drives is system of drives is
simultaneously moving the other simultaneously moving the other
connected system.connected system.
IDLER PULLEY
1) Adjust tension and slack in the belt
2) Increase the belt contact area with pulley
3) To make drive compact
APPLICATIONSAPPLICATIONS
DRILLING MACHINE DRILLING MACHINE WITH SPEED CONE WITH SPEED CONE PULLEYSPULLEYS
A OPEN BELT DRIVE IN A A OPEN BELT DRIVE IN A JIG-SAW MACHINEJIG-SAW MACHINE
LATHE MACHINE LATHE MACHINE WITH SPEED CONES WITH SPEED CONES AND TIMING BELTAND TIMING BELT
SKIVING MACHINESKIVING MACHINE
A PLANAR MACHINE A PLANAR MACHINE WITH GUIDE PULLEYSWITH GUIDE PULLEYS
A GUIDE PULLEY BELT DRIVE A GUIDE PULLEY BELT DRIVE IN SPINDLE MOULD MACHINEIN SPINDLE MOULD MACHINE
A FLAT BELT IN A CIRCULAR A FLAT BELT IN A CIRCULAR SAW MACHINESAW MACHINEA TIMING BELT IN LATHE MACHINEA TIMING BELT IN LATHE MACHINE
TIMING BELT OF AN AUTOMOBILESTIMING BELT OF AN AUTOMOBILES
IN SEWING MACHINEIN SEWING MACHINE
IN TREADMILLSIN TREADMILLS
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