POWER TRANSMISSION BY BELT DRIVE-FITTER ONLINE NOTE

INTRODUCTION OF POWER TRANSMISSION:-

i)- To start small or big machines some type of power is required like electric motor and engine etc. 

ii)- This power produces a rotational energy and to transfer this rotational energy from one place to another place .

iii)- It is a different accessories are required like pulleys, belts, chains and gears, etc.

iv)- The process of transfer of energy from one place to another place or from one device to another device is known as power transmission. 

v)- We know that energy can be produced by running electric motor, oil or steam engine etc. 

vi)- With that energy a machine or shaft can be operated.

vii)- In this system to move the shaft slow or fast different shape of small and big diameter pulleys or gears are fitted with this to pulley or gear.

viii)- motor shaft is called driver pulley or prime mover. The pulley rotated by driver pulley with the help of rope or belt is called driven pulleys or follower. 

ix)- The direction of rotation of driver and driven pulleys depend upon the direction of belt.
 

METHODS OF POWER TRANSMISSION:-

(1) By belt, (2) By rope , (3) By chain and sprockets, (4) By gears, (5) By friction, (6) By cam, (7) By clutching, (8) By shaft and coupling.

1. BY BELT

i)- It is a friction type drive because belt produces friction on pulley, by which power transmission is done.

ii)- If there is no friction then there will be no power transmission like loose belt will not rotate the pulley.

iii)- Belt has elastic therefore it can easily bend but its in disadvantages is that it has creep-age and slippage.

iv)- That is why constant velocity ratio is not obtained.

v)- Belts are made by Leather, Cotton or Canvas, Rubber, Nylon . 

Types of belts according to working:-

i)- The choice of a particular belt depends upon speed ratio, center distance, flexibility, strength, economy and maintenance consideration of the driving system.

ii)- Basically five types of belts are used for the transmission of power a)- Flat belt, b) - V-belt and multiple V-belt, c)- Ribbed belt, d)- Toothed or timing belt, e)- Link belt .

Method of power transmission by belt:-

1. Open Belt Drive: 

i)- In this system drive and driven pulleys are connected together by open belt. 

ii)- In this system both the pulleys rotate in same direction and both the shafts are in parallel to each other. It is also called straight or open Belt drive.

(2) Cross Belt drive:

 i)- In this system drive and driven pulleys rotate in opposite direction to each other .

ii)- The belt cross on both pulleys and shafts are in parallel to each other.

(3) Quarter Twist Drive: 

i)- This system is used in such places where both shafts are is not in one axis line and cross cut each other.

ii)- If pulleys are to rotate at special angle then this system is used.

(4) Right Angle Belt Drive: 

i)- This system is used where pulleys are fitted at right angle to each other.

ii)- In this system  two socket pulleys are fitted in it.

iii)- In this system belt is moved on inside of one socket pulley and outside in another pulley. 

iv)- This system is also used to transfer power at right angle or at special angle.

(5) Jockey Drive: 

i)- During transmission of power driver pulley and driven pulley distance from center to center should not be less than three times of bigger pulley diameter.

ii)- The diameter of both pulleys ratio should not be more than 6:1. 

iii)- If this ratio is increased than arc of contact of belt on face of pulley decrease so to increase this another small pulley is used know as jockey pulley.

iv)-  Its another name is Idler pulley.

v)- This pulley increase the rapping angle and belt tension for transmission of torque.

(6) Stepped Drive:-

i)- Stepped drive is used to increase or decrease the speed in power transmission.

ii)- Its changing the belt on pulleys different speed can be obtained.

FORMULA TO TAKE LENGTH OF BELTS

1. Find out the length of belt in open belt drive:

A)- Formula: 

L = 2.C+ 1.57 (D +d) + (D-d)2/4C

L= Length of belt

C = Center distance between two pulleys

D = Diameter of big pulley

d = diameter of small pulley

OR

B)- Formula:

L = 2.C+13 (R+r)/4

R = Radius of big pulley

r = radius of small pulley

C = Center distance between two pulleys

2) Find out the length of belt in Cross Belt Drive:

A)- Formula:

L = 2.C+ 1.57 (D + d) +(D+d)2/4.C

Formula:

L = Length of belt

C = Center distance between two pulleys

D = Diameter of big pulley

d = diameter of small pulley

OR

B)- Formula:

L = 2.C+ 27(R+r)/8

R = Radius of big pulley

r = radius of small pulley

C = Center distance between two pulleys

Example 1: Find the length of belt in open belt drive. When dia. of pulley fitted on main shaft is 200 mm and motor shaft pulley diameter is 250 mm. The Center distance between two pulleys is 4 metre.

Solution:

Dia. of motor shaft pulley ( D)= 250 mm

Dia. of main shaft pulley (d) = 200 mm

Center distance between two pulleys (C) = 4 metre

Formula in open belt drive: L = 2.C+ 1.57 (D +d) + (D-d)2/4.C

L = 2 x 4000 + 1.57 (250 + 200)+ (250 - 200)2/4 x 4000 

= 8000 + 1.57 x 450 + (50)2/1600

= 8000 + 706.5 + 0.156

= 8000 + 706.50 + 5/32

= 8706.650 mm or 8.7066 m Ans.