STUDY OF POWER TRANSMISSION SYSTEMS

INTRODUCTION TO MECHANICAL DRIVES: -

The mechanical power produced by prime mover is used to drive various machines in

the workshops and factories. The transmission of power from prime mover to machine can be

obtained by two systems.

1) Individual Drive

2) Group Drive

1) Individual Drive: -

This drive is known as self-contained drive because there is separate prime mover for

each machine. Generally motor and starter are provided for individual machine.

Applications: -

i) Mobile or portable machine.

ii) In workshops having few machines.

iii) When overhead face is required for the cranes.

iv) It is suitable when machine is likely to be shifted at different places.

2) Group Drive: -

A single motor or prime motor of large capacity drives a common overhead main shaft

located from one end of the workshop. This shaft has many pulleys. The motion is

transmitted from this shaft to individual machines by flat belt and pulley systems.

Applications: -

i) Process industries.

ii) For operating machines which are arranged to perform sequential operations.

CLASSIFICATIONS OF POWER TRANSMISSION SYSTEMS: -

The mechanical power from prime-mover to machine or from one shaft to the other can

be transmitted by following methods.

i) Shaft Drive.

ii) Friction Drive.

iii) Coupling.

iv) Belt Drive.

v) Rope Drive.

vi) Cultch Drive.

vii) Gear Drive.

viii) Chain Drive

The important types are discussed below:

1) Belt Drive: -

i) This is the most commonly used method of power transmission in which the

two shaft are rotated by an endless, thin belt running over the two pulleys on the

shafts.

ii) The pulley on driving shaft is known as driver where as pulley on the other

shaft, to which power is transmitted is known as driven pulley or follower.

There are four types of belt drive.

a) Open Belt Drive: -

In this drive to parallel shafts are connected by belts such that driver and follower both

rotate in same direction as shown in fig.

b) Cross Belt Drive: -

The two parallel shafts are connected by belt-pulleys such that the follower pulley

rotates in the direction opposite to that of driver pulley in this drive.

c) Quarter Turn Drive: -

The two nonparallel and non – intersecting shafts can be connected by belt and pulley.

d) Right Angle Drive: -

In this, additional guide pulley is used to direct the belt and to adjust tension of the belt,

which connects the two non – parallel shafts.

Belt Shapes :

The cross-section of the belts is commonly of three types

i) FLAT BELT :-

This belt is flat with small thickness. The pulley surface is also flat and the width of pulley is

¼ th greater than the belt width.

ii) ‘V’ BELT :-

It is trapezoidal in section placed in a ‘V’ shaped groove of grooved pulleys. It is made of

fabric with a cotton chord tension element. It is used for large power transmission, for short

distances between the shafts.

iii) ROUND BELT: -

It is a rope cord and this drive is called as rope drive. The cross-section of this belt is round.

These ropes are passed in the grooves of the pulleys. It is suitable for moderate distances and

separate drives can be taken from one driving pulley.

Applications of Belt Drives: -

i) Flour mills and grinding mills.

ii) For pumping water from the well.

iii) Line shaft driving and group drive.

iv) Stepped pulley driving and group drive.

v) ‘V’ belt drive fro radiators and compressors.

Types of Pulleys :-

The pulleys are made of cast iron wrought iron, pressed steel and wood.

i) Fast and loose pulleys.

ii) Speed cones or stepped pulleys.

iii) Guide pulleys.

iv) Grooved pulleys.

v) Jockey pulleys or Rider pulleys.

vi) Wrought iron pulleys.

2) Chain Drive :-

i) In this drive, rigid links are hinged together to form a chain as shown in

fig.

ii) The chain links provide flexibility for wrapping the chain over the special toothed

wheels.

iii) These wheels are known as chain sprockets. They are very similar to spur

gears.

iv) Sufficient lubrication is required for this drive to avoid wear and tear also

noise.

v) Chain drives are replacing belt or rope drives and wheel gearing.

There are two types of chains: –

i) Roller chain for slow speeds and

ii) Silent chain for high speeds.

Application of Chain Drives: -

i) Used for short distance for transmitting hung power up to 4000 kw with large

transmission numbers (up to 15).

ii) They are used in agricultural and sugar machinery where the centre distance is

moderate or large up to 8m.

iii) Cycles, motors-cycles, motor vehicles etc.

iv) Road rollers, workshops and factories.

3) Gear Drive :-

i) Gears are toothed wheels the teeth of gear engage in the teeth of follower gear for power

transmission.

ii) For obtaining desired speed and direction of rotation gear trains of many gear wheels are

used.

iii) Different types of gears are used for connecting parallel, non-parallel, intersecting and

non – intersecting shaft.

iv) Center distance between the shaft should be very small.

Types of Gears: -

The different types of gears are bellow-

i) Spur Gear ii) Spiral Gear iii) Helical Gear

iv) Bevel Gear v) Worm and Worm Wheel vi) Rack and Pinion.

I) SPUR GEAR:-

Spur Gears are used when the axis of two shafts are parallel to each other. These gears

have teeth parallel to the axis of shaft.

Advantages:

Simple in manufacturing.

Cheaper than other types of gears.

Interchangeability is possible.

Disadvantages:

Load carrying capacity is low.

Transmission efficiency is low.

Speed reduction is low.

Applications:

Used in automobile gearbox, machine tools and all low power transmission application.

III) HELICAL GEARS

In helical gears, teeth are at some angle called helix angle with respect to axes of the

shaft.

Helical gears run quieter as compared to spur gears since the contact between teeth is

gradual. Therefore transmission of load is gradual which results in low impact stresses

and reduction in noise. For this reason the helical gears are used for high-speed

transmission.

Advantages:

Load carrying capacity is high.

Transmission efficiency is high.

High-speed reduction is possible.

Disadvantages:

Manufacturing processes is difficult.

Cost is high.

Interchangeability is not possible.

IV) WORM GEAR :-

Worm gear is used when the two shafts are non – intersecting at right

WORM AND WORM WHEEL

Worm and worm wheel are used to transmit power from one shaft to another shaft which

are non-intersecting and their axis are normally right angles to each other. Worm and

worm wheel are used for large speed reduction up to 100:1.

Advantages:

High speed reduction ratio is possible up to 100:1

Quieter in operation.

Provision of self-locking is possible.

Disadvantages:

Manufacturing processes is difficult.

Cost is high.

Interchangeability is not possible.

Transmission efficiency is low.

Application:

Used in materials handling equipment, lifting equipments, cranes and all applications

where high-speed reduction is required.

a. RACK AND PINION:-

It convert rotary motion into straight line motion and vice versa.

It is used in lathes, drills, planners etc.

Advantages :-

It is gives smooth and silent operation.

It is extremely strong and durable.

It gives long service without any attention.

High power transmission.

Suitable for precision and accurate speed control.

Disadvantages :-

It is very costly.

It should be well lubricated.

STUDENTS SHOULD UNDERSTAND FOLLOWING POINTS:

1) Classification of Power Transmission Systems.

2) Application of Various Power Transmission Systems.

3) Different Types of Gear Trains.

ASSIGNMENTS:

1) Explain Different Belt Drive Systems.

2) Draw Sketches of Any Two Types of Chain Drive.

3) Give Advantages, Disadvantages & Application of Gear

Trains.

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