Definition of a belt
Belt is in the form of a loop. It connects mechanically two shafts for transmitting power smoothly. A belt drive consists of shafts,pulleys and a belt.
MATERIALS OF BELTS
Standard Thicknesses of belts
5, 6.5, 8, 10 and 12 mm are the standard thicknesses.
Standard widths of flat belts
25, 32, 40, 50, 63, 71, 80, 90, 100, 112, 125, 140, 160, 180, 200, 224, 250, 280, 315, 400, 450, 500, 560 and 600 mm
TYPES OF FLAT BELTS
- Based on Orientation
- Quarter –turn
- Reversed drive
- Based on Load or duty or power to be transmitted
|Sr. No.||DUTY or LOAD||Power||Peripheral velocity|
|1.||Light load||7.5 kW||12 m/s|
|2.||Medium Load||7.5 to 15 kW||>12|
|3.||Heavy load||> 15 kW||>24 m/s|
Important terminology for belts
(i) Speed ratio
Neglecting the slip and thickness of the belt.
Speed ratio= diameter of bigger pulley/diameter of smaller pulley
Hence Speed ratio = N1/N2
Where N1 is the motor or engine speed OR higher speed
N2 is the machine speed or lower speed
(ii) Center distance
(iii) Peripheral velocity
LAW OF BELTING
The center line of belt as it approaches the pulley must coincide with the central plane of that pulley. Otherwise belt will fly away from the pulley.
TYPES OF PULLEYS USED WITH BELTS
There are two types of pulleys used with belts.
(I) Flat pulleys——–Used with flat belts.
(ii) Grooved pulleys—–Used with V-belts. Grooved pulleys are called sheaves.
Belt Drive and its Types
A belt drive consists of two shafts, two pulleys and a belt. One of these shaft is a motor shaft on which electric motor is mounted. On the other shaft the machine is mounted to which power is transmitted by the belt drive. Belt drive is used to transmit power from the motor to the machine shaft. It can be from the engine to the machine shaft. This can also be from turbine to generator.
Normally speed of the motor is high because high speed motors are more efficient. Therefore motor shaft is the driving shaft and the machine shaft is the driven shaft. Therefore, in most of the cases the machine has Lesser RPM than that of the motor. Therefore pulley on motor will be smaller pulley and the pulley on the machine will be a larger pulley. Belts do not transmit with 100 % efficiency because of SLIP and stretching of the belt.There are two types of belt drive, namely flat belt drive and V-belt drive.
Cross Belt Drive
Advantages of a belt drive
- Belt drive is a simple drive.
- It is cheap.
- No lubrication required.
- Have high efficiency.
- Requires less maintenance.
- Some misalignment is adjustable without loss in efficiency.
- Durable and has long life.
- Can be used for parallel and non parallel shafts.
- Easy to reduce vibrations and noise.
Disadvantages of a belt drive
- Velocity ratio is not truly constant because of slip and stretching.
- Heating occurs due to friction. It disturbs its perfect working at higher temperatures.
- There is a speed limit of 35 m/s.
- Requires center distance adjustment due to stretching.
PRACTICAL APPLICATIONS OF A FLAT BELT DRIVE
(ii) Water pumps
(iv) Saw mills
(v) Electrical generators
PRACTICAL APPLICATIONS OF A V- BELT DRIVE
(i) Stone crushers
(ii) Machine tools
(iii) Paper industry
(iv) Textile industry
(v) High power mills
(vi) Refrigeration and air conditioning machinery