ME 6601 - DESIGN OF TRANSMISSION SYSTEMS unit -1 Introduction to Flexible drives

1. DEPARTMENT OF MECHANICAL ENGINEERING
SUB CODE & NAME : ME 6601- Design of Transmission Systems
INTRODUCTION TO FLEXIBLE DRIVES
By
Mr. B.Balavairavan
Assistant Professor
Mechanical Engineering
Kamaraj College of Engineering and Technology
Virudhunagar

2. Transmission Systems
Transmission systems transfer mechanical power from a source to another machine
components.
For example In a car, power from engine is transmitted to wheels through clutch,
gearbox, prop shaft and differential, these components are called transmission
elements.
If we consider a lathe, power from motor is provided to a chuck through belt drive
and gearbox, these components are transmission elements.
Flexible Drives (Belt, Chain etc)
Rigid Drives (Gears,Motion control elements (Brakes,Clutches etc)

3. Flexible Drives
Belts, Chain and Wire Rope Drives are flexible yet capable of transmitting
power.
They are simple in construction and cost effective.
Primitive elements for power transmission.
Classification of Flexible Power Drives
1. Belt Drives
2. Wire Ropes
3. Chain Drives

4. History of Flexible Drives
Babylonians and Assyrians used chains
for the first time for water drawing
machines.
By 1430, rope was used to drive
grinding devices.
In the 18th century - with invention of
steam engine, the power transmission
drive with flat belts made of chrome
leather became the indispensable basis
for industrial production.

5. Advantages and Disadvantages
Advantages
1. Transmits power between long
distance compared to rigid
elements
2. Absorbs shock loads and
provides damping
3. The operation is smooth and
silent
4. Provides simple machine design
5. Comparatively cheaper
Disadvantages
1. More space required
2. Velocity ratio is comparatively
small.
3. Power transmission varies if
overloaded.

6. Belt Drives
Belt drives are commonly used to
transmit power between two
shafts which are separated at
distance.
The belts run over pulleys, the
pulley connected with the
source of power is called the
driver pulley and the other
pulley is a called a driven.
Sometimes belt drives may have
idler pulleys also.

7. Belt Types - Cross Section

8. Belt Types - Drives
Open Drive Crossed Drive
Quarter Turn
With Idler Pulley

9. Belt Materials
1. Leather belt
2. Nylon-Core belt
3. Rubber belt
4. Cotton and Canvas belt
5. Balata Belting
6. Rubber on fabric belt ,etc.,

10. Advantages of Belt Drives
Belts permit flexibility ranging from high horsepower drives to slow speed and
high speed drives.
Belt drives are less expensive than chain drives.
Belts require no lubrication.
Single belt drives will accept misalignment than chain drives.
Flat belts are best for extremely high speed drives.
Belt drives cushion shock loads and load fluctuations.
Belts will slip under overload conditions, preventing mechanical damage to
shafts, keys, and other machine parts.

11. Disadvantages of Belt Drives
Belts cannot be used where exact timing or speed is required because slippage
does occur (only timing belts can be used).
Belts are easily damaged by oil, grease, abrasives, some chemicals, and heat.
Belts can be noisy; also loose or worn belts can be a major cause of machinery
vibration

12. Tight Side and Slack Side
When belt is running over pulley, the
friction creates grip on pulley which
creates tension on one side of belt which
makes the driven pulley to run, this side
is called tight side. The other side does
not experience same tension, that side is
called slack side.

13. Law of Belting
The centerline of the belt as it approaches the pulley must lie in a plane
perpendicular to the axis of the pulley, or must lie in the plane of pulley,
otherwise the belt will run of the pulley.
Velocity Ratio

14. Belt Creep
As the belt moves from slack side to
tight side the tension increases. That
is tension is less in slag side and high
in tight side. This results in
elongation of belt in tension side
resulting in less thickness on tension
side. This is called creep

15. Belt Wipping
As the distance between the pulley driven by belt increases, the belt begins to
vibrate in the direction perpendicular to the direction of motion of the belt drive.
This vibrations of belt drives is called wipping.

16. Centrifugal Tension in Belt
When the belt runs round the pulleys, a centrifugal force is produced on the belt.
This force tends to lift the belt from the pulley surface, resulting in more
tension on belt.

17. Belt Slip
Slip is a type of loss occurring in belt drives. When the friction force between the
pulley and belt is less, the belt moves without rotating the pulley or pulley rotates
without pulling the belt.