1. FUNDAMENTAL UNDERSTANDINGFUNDAMENTAL UNDERSTANDING
OFOF
PULLEYS AND BELTDRIVESPULLEYS AND BELTDRIVES
ELEMENTS OF TECHNOLOGYELEMENTS OF TECHNOLOGY

2. WHAT ARE BELT DRIVESWHAT ARE BELT DRIVES
 A belt drive is a method of transferring rotary motion betweenA 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 moreA 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 theThe 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 toA 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 aroundA 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.

3. TYPES OF BELTSTYPES OF BELTS
There are 4 types belts used in belt drives they are as follows:
Flat belts
shaft 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

4. ROUND BELTROUND BELT
 Round belts are a circular cross section beltRound belts are a circular cross section belt
designed to run in a pulley with a circular (ordesigned to run in a pulley with a circular (or
near circular) groove.near circular) groove.
 The circular belt or rope is mostly used in theThe circular belt or rope is mostly used in the
factories where a great amount of power is tofactories 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 meterswhen the two pulleys are more than 5 meters
apart.apart.
FLAT BELTSFLAT BELTS
 Flat belts find their widest applicationFlat belts find their widest application
where high-speed motion, rather thanwhere high-speed motion, rather than
power, is the main concern.power, is the main concern.
 Flat belts are made from leather, wovenFlat belts are made from leather, woven
cotton, rubber, balata (wood gum).cotton, rubber, balata (wood gum).

5. ‘‘V’ BELTSV’ BELTS
 The strength of these belts is obtained byThe 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 atV-belts are far superior to flat belts at
small center distances and high reductionsmall center distances and high reduction
ratios.ratios.
 Require larger pulleys than flat beltsRequire larger pulleys than flat belts
because of their greater thickness.because of their greater thickness.
 TheThe "V""V" shape of the belt tracks in ashape 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.

6. TIMING BELTSTIMING BELTS
 Also known asAlso known as ToothedToothed,, NotchNotch oror CogCog
belts are abelts are a positivepositive transfer belt and cantransfer belt and can
track relative movement.track relative movement.
 These belts have teeth that fit into aThese belts have teeth that fit into a
matching toothed pulley .matching toothed pulley .
 They are often used to replace chains orThey are often used to replace chains or
gears, reducing noise and avoiding thegears, reducing noise and avoiding the
lubrication bath or oiling systemlubrication bath or oiling system
requirement.requirement.
 Requires the least tension of all belt drivesRequires the least tension of all belt drives
and are among the most efficient.and are among the most efficient.

7. 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 DRIVESTYPES OF BELT DRIVES
BASED ONBASED ON
ARRANGEMENTARRANGEMENT

8. OPEN BELT DRIVEOPEN BELT DRIVE
 The Open belt drive is arranged withThe Open belt drive is arranged with
shafts arranged parallel and rotating inshafts arranged parallel and rotating in
the same direction.the same direction.
 The driver pulls the belt from one sideThe driver pulls the belt from one side
and delivers it to the other side thus theand delivers it to the other side thus the
tension in the one side belt will be moretension 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
2
1
1
dr =
2
2
2
dr =
x
x
dd rr )22(
2
2
)( 2121 +
++
+π
Length of the open belt=Length of the open belt=

9. CROSSED OR TWIST BELT DRIVECROSSED OR TWIST BELT DRIVE
 The crossed or twist belt drive isThe crossed or twist belt drive is
used with shafts arranged parallelused with shafts arranged parallel
and rotating in the oppositeand rotating in the opposite
directions.directions.
 The tension in the tight side will beThe tension in the tight side will be
more than the slack side. Themore than the slack side. The
point where the belts rubs againstpoint where the belts rubs against
each other and there will beeach other and there will be
excessive wear and tear.excessive wear and tear.
 To avoid this the shafts should beTo avoid this the shafts should be
placed at a maximum distance ofplaced at a maximum distance of
20b where b is the width of the20b where b is the width of the
belt and the speed should be lessbelt and the speed should be less
than 15 m/s.than 15 m/s.
X
2
1
1
dr =
2
2
2
dr =

10. Length of the cross belt=
x
rr
x
dd )22(
2
2
)( 2121 −
++
+π
Velocity of Belt (V)=
60
dN×π Where ( 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 ××− π
Power (P) =
45000
dNTπ
Here ( d=diameter in meters, N=Speed in RPM,
P=power in HP (Horse Power),
T= Tension in the belt in Kgs )
Power (P) =
60
11NdTπ Here ( d1=diameter in meters, N1=Speed in RPM,
P1=power in Watts,
T= Tension in the belt N )

11. COMPOUND BELT DRIVECOMPOUND BELT DRIVE
 A compound belt drive is usedA compound belt drive is used
when power is transmitted fromwhen power is transmitted from
one shaft to another through aone shaft to another through a
number of pulleys.number of pulleys.
 The belts are connected in suchThe belts are connected in such
a way that the driver moving onea way that the driver moving one
system of drives issystem of drives is
simultaneously moving the othersimultaneously moving the other
connected system.connected system.

12. IDLER PULLEY
1) Adjust tension and slack in the belt
2) Increase the belt contact area with pulley
3) To make drive compact

13. APPLICATIONSAPPLICATIONS
DRILLING MACHINEDRILLING MACHINE
WITH SPEED CONEWITH SPEED CONE
PULLEYSPULLEYS
A OPEN BELT DRIVE IN AA OPEN BELT DRIVE IN A
JIG-SAW MACHINEJIG-SAW MACHINE
LATHE MACHINELATHE MACHINE
WITH SPEED CONESWITH SPEED CONES
AND TIMING BELTAND TIMING BELT
SKIVING MACHINESKIVING MACHINE

14. A PLANAR MACHINEA PLANAR MACHINE
WITH GUIDE PULLEYSWITH GUIDE PULLEYS
A GUIDE PULLEY BELT DRIVEA GUIDE PULLEY BELT DRIVE
IN SPINDLE MOULD MACHINEIN SPINDLE MOULD MACHINE
A FLAT BELT IN A CIRCULARA FLAT BELT IN A CIRCULAR
SAW MACHINESAW MACHINEA TIMING BELT IN LATHE MACHINEA TIMING BELT IN LATHE MACHINE

15. TIMING BELT OF AN AUTOMOBILESTIMING BELT OF AN AUTOMOBILES

16. IN SEWING MACHINEIN SEWING MACHINE

17. IN TREADMILLSIN TREADMILLS