Flat Belt

Flat belts are usually made of leather, rubber and fabric. belts made of leather has high coefficient of friction (can transmit more power) thereby ideal for flat belts.  To achieve the desired thickness of belt, number of layers of belt material is cemented together.

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Usually the top and bottom layers are made of leather or rubber which has high coefficient of friction and also it acts as a protective layer. The inside layers are made of canvas, fabric or other material which transmits the majority of the load handled by belt.

Number of plies in flat belts (ply)

A number of layers of belt material is cemented together to achieve the desired thickness of belt. The layer of belts is called as ply. The total number of belt layers used in a belt is called number of plies.

Properties of a flat belt material

  1. The material from which belt is made of should have high coefficient of friction.
  2. To withstand the tensions created, the belt material should have high tensile strength.
  3. When belt passes through pulley bending stress is induced, to avoid this this the material should be flexible and should not be rigid.
  4. The material should have water resistance.

Advantages of flat belts

      The efficiency of flat belts in 98%, which is equal to that of gears.

      They have high load carrying capacity.

      They can be employed where high operating speed is required.

      They produce less noise compared to v-belts.

      They can absorb shock loads compared to v-belts. 

Disadvantages of flat belts

  1. Flat belts can not be operated on small diameter pulleys.
  2. If the working environment is corroding the belt life decreases.

Flat Belt Selection - Using PSG Design Data Book

 Step:1

Selection of standard pulley diameters

  

Calculate the diameters of the smaller and larger pulley using the relation

Then select the standard pulley diameters from PSG 7.54

 


  - Diameter of larger pulley (mm)
  - Speed of the larger pulley (rpm)
  - Diameter of small pulley (mm)
  - Speed of the small pulley (rpm)
  - velocity ratio

 Step:2

Calculation of design power

  

For calculating design power select,

  1. The load correction factor from PSG 7.53
  2. The arc of contact factor from PSG 7.54 using the arc of contact value
  3. Small diameter factor from PSG 7.62

Calculate the design power using the formula

 

 




 Design Power - (kW)
 Rated power - Power of motor (kW)

 Step:3

Selection of belt

  

Select the type of belt from PSG 7.52
 

 

 Step:4

Load Rating and Number of plies

  

Load Rating
Calculate the velocity of belt / belt speed using the formula

Then calculate the load rating using the formula in PSG 7.54

  

Number of plies
Select the number of plies required from PSG 7.52

  

 



  - Diameter of small pulley (mm)
  - Speed of the small pulley (rpm)
 -Velocity of belt of speed of belt (m/s)
 Load rating - (kW/mm/ply)

 Step:5

Belt Width

  

Calculate the belt width using the formula

Select the standard belt width from PSG 7.52

  

 

 Design Power - (kW)
 Load rating - (kW/mm/ply)
 Width of belt - (mm)

 Step:6

Pulley Width

  

Calculate the pulley width using the condition in PSG 7.54

 

 

 Pulley width - (mm)

 Step:7

Length of Belt

  

Calculate the belt length using the condition in PSG 7.53

 

 Belt length - (mm)