unit-i power transmission devices...roller chain • roller chain consists of five parts : 1. outer...

UNIT-I

POWER TRANSMISSION DEVICES

BELT DRIVES

• A belt is a flexible mechanical element that transmit the power from one shaft to other.

• A belt drives make use of belts to, mechanically link two or more rotating shafts & transmit continuous power.

• Belt drives smoothly transfer power from driving shaft to driven.

Prepared By: Prof. Shyam S. Darewar

TYPES OF BELTS

Flat Belt:

• Shaft distance 5 to 10m.

• Low power and high speed.

V-Belt:

• Shaft distance less than 2m.

• High power moderate speed.

Round Belt: • Shaft distance >5m. • Small initial tension • Absence of vibration and noise. • High Power

Timing Belt: • Positive drive. • Precise. • reliable


TYPES OF BELT DRIVES

FLAT BELT DRIVES:

Open belt drive:

Axis of pulleys are parallel to each other.

It transmit the power by using friction produced between belt and pulleys.

Rotation of the pulley is in the same direction.

In order to avoid slipping of the belt from the pulley it is provided with the crown.

Example: belt transmission in automobile (scooties), floor mill.

Crowned Pulley



FLAT BELT DRIVES:

Cross belt drive:

It is similar to the belt drive but the difference between these two belt drives are in cross belt drive the direction of rotation of pulleys are opposite to the each other.

Here the pulleys are sets up at the offset position by providing some miss alignment between two pulleys.



FLAT BELT DRIVES:

Quarter turn belt drive:

Two axes of pulleys are right angle to each other.

Used in industries for parallel transmission to tangential position.

Guide pulleys are provided to increase tension in the belt.



FLAT BELT DRIVES:

Compound belt drive:

Compound belt drive is used to transfer power from one shaft to the other through number of pulleys.

The belts are connected in such a way that the driver moving one system of drives is simultaneously moving the other connected system.


SPEED RATIO (VELOCITY RATIO) OF BELT DRIVE

Speed ratio or velocity ratio of the belt drive is the ratio of speed of the driving pulley to the speed of the driven pulley.

Let, d= diameter of the driving shaft in mm D= diameter of the driven pulley in mm n = speed of the driving pulley in r.p.m N = speed of the driven pulley in r.p.m. t = thickness of the belt in mm V = linear speed of the belt in mm/sec i = Speed ratio or velocity ratio Prepared By: Prof. Shyam S. Darewar

SPEED RATIO (VELOCITY RATIO) OF BELT DRIVE

Linear speed of the belt V= πdn/60 or………………(i) V= πDN/60………………….(ii)

From equation i and ii πdn/60 = πDN/60

Therefore, n/N = D/d As i= speed of the driver pulley/ speed of the driven pulley

i= n/N=D/d If the thickness of the belt an torque on the both pulleys are considered, then,

Speed ratio, i=n/N=(D+t)/(d+t)=TD/Td Where, TD = Torque on the driven pulley in N-m Td = Torque on the driving pulley in N-m


Advantages of Belt Drives:

They are simple and economical.

They can transmit power at the considerable distance.

They can protect the machine from overloading by slipping of the belt over pulley.

Belt drive can absorbs shocks and can damp the vibrations.

The operation is smooth and silent.

They are durable and requires very little maintenance.


Disadvantages of Belt Drives:

Limited speed range.

They are not compact.

Considerable power loss.

The velocity ratio may vary due to the belt slip.

They inflict heavy load on shaft and bearing.

Require more space for installation.


Chain Drive

• The main disadvantage of the belt drives and the rope drives is that the velocity ratio does not remain constant, but varies on account of slip. Since chain drives are positive drives there is no slip, hence the velocity ratio will remain constant.

• Chain drives are suitable for small centre distances and can be used generally up to 3 meters but in special cases even up to 8 meters. Chain drives transmit power up to 100kw and operating peripheral velocity up to 15m/s. The velocity ratio can be as high as 8:1.


https://www.theengineerspost.com/types-of-belt-drives/





https://www.theengineerspost.com/rope-drive/





https://en.wikipedia.org/wiki/Velocity















Roller Chain

• Roller chain consists of five parts : 1. outer link plate 2. inner link plate 3. pins 4. bushings 5. rollers.

• Two rows of the outer link plates and inner link plates. • The bushings are press fitted into inner link plates. • The pins, which passed through the bushings are pressed into the outer link plates. • The rollers are fitted on the bushings, and can turn freely on it. • The outer link plates are free to swivel with respect to the inner link plates. • Power is being transmitted by mounting chain on the sprockets. • Applications: Bicycle, motor cycle, agricultural machinery, rolling mills, conveyors etc

Advantages of Roller Chain

• Positive drive, only 6% power loss occurs during power transmission.

• Can be used for short as well as long distances.

• The chain drives are compact as compare to the belt drives.

• The chain can operated high temperature then belt.

• Easy for maintenance and replace.

• Easy to manufacture.

• Easy to obtain different gear ratios with chain drive without jerk.


Disadvantages of Roller Chain

• Due to polygonal effect it is not used for precise motion transfer.

• Lubrication is required.

• Noisy in operation.

• Can lead to accident if failure occur due to locking of rear wheel.

• Regular maintenance is required.

• Regular cleaning and tensioning is required.

• Life of the chain drive is less as compared to belt drive.


Gear Drives

• It is a positive drive.

• Used for short shaft distances.

• Transmit power and rotary motion from driving shaft to driven shaft.

• Power and motion is transmitted through progressive engagement of the projection called ‘Teeth’.

• Profile of the gear tooth is either involute or cycloid.

• Always operates in pair.

• Smaller gear is termed as pinion while larger is a gear.

Types of Gears


Spur Gear Drive

• It is a parallel shaft gears.

• They have straight teeth's.

• More power loss due more contact area during engagement.

• Noisy in operation due to sudden engagement and disengagement.

• Simplest type of gear can not be used for precision power transmission.

• Spur gear pair can be used for reduction ratio upto 6:1.


Gear Drives Pitch Line Velocity:

• The pinion and gear rolls over each other, without slipping, along the pitch circle. Therefore the pith line velocity of gear and pinion is same. It is given by;


Gear Drives Speed ratio or gear ratio:

• It is the ratio of pinion speed to the gear speed. It can also be defined as the ratio of the number of teeth on the gear to the number of teeth on the pinion.


unit-i power transmission devices...roller chain • roller chain consists of five parts : 1. outer...

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