This document provides information and steps to design a flat belt drive system to transmit 20 kW of power at 720 rpm from a driving pulley to a driven pulley with a speed ratio of 3 and center distance of 3 meters. The standard pulley diameters are selected as 400 mm for the driver and 1200 mm for the driven pulley. The design power is calculated to be 25 kW considering a shock load, arc of contact of 164 degrees, and transmission ratio of 3. A 6-ply 112 mm wide Dunlop "FORT" belt is selected to transmit this power. The length of the belt is calculated to be 8566.6 mm. The pulley widths are selected as 125 mm with 4 arms for

1. 1
DEPARTMENT OF MECHANICAL ENGINEERING
PROBLEMS ON DESIGN and selection FLAT
BELT DRIVE using psg design data book
By
Mr. B.Balavairavan
Assistant Professor
Mechanical Engineering
Kamaraj College of Engineering and Technology
Virudhunagar

2. Number of plies (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.
2

3. Advantages of flat belts
1. The efficiency is 98%, which is
equal to that of gears.
2. High load carrying capacity.
3. Can be employed where high
operating speed is required.
4. They produce less noise compared
to v-belts.
5. 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.
3

4. Arc of Contact
The angle subtended by the belt on the pulley is know as angle of contact or arc
of contact. For better performance the angle of contact should be between 90° to
170°. To increase the angle of contact idler pulleys can be used.
4

5. Pulley Crown
To prevent the flat belts from running off, at least one of the pulleys has to be
crowned, preferably the larger pulley, or the pulley with the largest arc of
contact.
5

6. Belt Joints
Thermofix joining system
Thermofix is an adhesive bonded
joint.
Flexproof joining system
Flexproof is a fusion joint used without
the addition of adhesive.
6

7. Flat Belt
Selection using PSG design
data book
7

8. For the calculation of a two-pulley power transmission belt the
following data are required:
Motor power or power to be transmitted (in kW)
Speed of drives
Number of revolutions of driving pulley (n)
Number of revolutions of driven pulley (N)
Diameter of pulley
Diameter of driving pulley (d)
Diameter of driven pulley (D)
Transmission ratio or velocity ratio (i)
Center distance (C)
8

9. Procedure Stages
1.Selection of std. pulleys.
2.Design Power Calculation.
3.Selection of Belt.
4.Calculating Load Rating and required Number of Plies
5.Selecting Belt Width
6.Calculating Length of Belt.
7.Pulley Dimensions - Width, No. of Arms, Crowning. 9

10. Problem 1
Problem Statement:
A belt is to transmit 20 kW at 720 rpm to
a rolling machine with a speed ratio of 3.
Center distance between the pulleys is 3
m. Design a suitable belt drive if the
rolling machine pulley diameter is 1.2 m.
Given Data:
Power = 20 kW
Driver speed (n) = 720 rpm
Transmission ratio (i) = 3
Centre Distance (c) = 3 m
Driven Pulley Diameter (D) = 1.2 m
10

11. Step - 1 “Selection of Std. Pulleys”
3 =
d
1200
d = 400 mm
11

12. d = 400 mm
D = 1200 mm
from page no: 7.54
Standard pulley diameters are
12

13. Step - 2 “Design Power Calculation”
13

14. from page no: 7.53
The Load is shock load for
rolling mills
Load Correcting factor = 1.5
14

15. from page no: 7.54
Arc of contact =
3000
1200 - 400
x 60 ൦180 ൦ -
= 164 ൦
Arc of contact factor = 1.04
for arc of contact 164 ൦
15

16. from page no. 7.62
for transmission ratio “i = 3”
Small pulley diameter factor = 1.14
16

17. Design Power =
1.04 x 1.14
25
= 25 kW
x 1.5
17

18. Step - 3 “Selection of Belt”
from page no: 7.52
Dunlop “FORT” Belt is selected based on load type
18

19. Step - 4 “Load Rating and No. of Belt Plies”
from page no: 7.54
V =
= 15.08 m/s
x n
60
𝜋 x d
=
x 720
60
𝜋 x 0.4
Load rating =
10
0.0289 x
= 0.04358 kW/mm/ply
15.08
19

20. from page no: 7.52
based on the values of
V = 15.08 m/s
d = 400 mm
No of plies = 6
20

21. Step - 5 “Selection of std. belt width”
from page no: 7.52
Width of pulley =
.04358 x 6
25
= 95.60 mm
for FORT type & 6 ply belt
Std. Width of belt = 112 mm
21

22. Step - 6 “Calculation of Belt Length”
from page no: 7.53
Length of belt =
4 x 3000
2 x 3000 +
= 8566.6 mm
2
𝜋 (1200+400)+ (1200+400)2
for open belt drive,
22

23. Step - 7 “Pulley Dimensions”
from page no: 7.54
Pulley width = 112 +13
=125 mm
from page no: 7.55
Std. pulley width = 125 mm
Width of Pulley
23

24. from page no: 7.56
for small pulley, 4 arms
for larger pulley, 6 arms
No of Arms
24

25. from page no: 7.55
for small pulley, (d= 400 mm & pulley width = 125 mm)
for larger pulley, (D= 1200 & pulley width = 125 mm)
Crowning of pulley
h = 1 mm
h = 1.2 mm 25