Design an Idler for a Conveyor Belt System
The
idlers are an important part of a belt conveyor system; they provide stability
to the conveyed materials. There are mainly three types of idles used in the
industry namely, flat idlers, trough idlers, and garland idlers. In this
article we will discuss only the flat type belt conveyor idler design.
The Basics of Flat Idler Design
Typically,
the following inputs are used for starting up the design process of the flat
idler:
○ Capacity of the
conveyor generally expressed in tons per hour.
○ Bulk density of the
conveyed materials generally expressed in tons per cubic meter.
○ Conveyor belt width
generally expressed in meters.
○ Belt speed generally
expressed in meters.
The
output aims from the design process are:
○ The spacing of the
idlers generally expressed in meters.
○ The idler speed
generally expressed in meters per second.
○ Load on each idlers.
○ Idler diameter
generally expressed in meters.
The
following design equations are used across the industry for calculating the
different design parameters of the flat idlers:
○ Spacing of the idlers
S =
(8*T1*H)/ (mb+ml)*g
..1.1
Where,
S is in
meters
T1= Belt
tension near the idlers as shown in the picture (N)
H=Belt
sag (m)
mb = weight of the belt (kg/m)
ml =Weight of the conveyed material (kg/m)
g
=Acceleration due to gravity
○ The weight of the
conveyed material can be further calculated as
ml= (10*W)/ (36*V)
1.2
Where,
mb is in kg/m.
W =
Capacity of the conveyor (tons per hour)
V = Belt
speed (m/sec)
○ Idler speed
N =
(60*V)/ (Π*D)
1.3
Where,
N is in
RPM.
V = Belt
speed (m/sec)
D =
Diameter of the idlers
Loads on
each idlers
○ F= (10*W*S*g)/
(36*V)
1.4
Where,
F is
in Newtons
g =
Acceleration due to gravity
W =
Capacity of the conveyor (tones per hour)
S =
Spacing between the two idlers.
V = Belt
speed (m/sec)
○ Maximum bending
stress on the idlers
b=
(8*F*L)/ (3*Π*D3)
..1.5
Where,
b is in Newtons per
square meter
F = loads
on each idlers (Newton)
L =
length of the idlers (Meter)
D =
diameter of the idlers (meter)
One Practical Belt Conveyor Idler Design Example
Now,
lets see how to use the basic design equations for actual design purpose. We
will take the following data as input:
Capacity
of the conveyor W = 1000 t/h
Belt
speed V =1.68 m/sec
Belt
tension near idler T1=50000 N
Idler
length L =1.2 m
Belt sag
= 0.015 m
Weight of
the belt mb=15
kg/m
Idler
speed N= 50 rpm
Design
procedure:
○ First, we will
calculate the weight of the conveyed material using the eqn.1.2 as:
ml = (10*1000)/(36*1.68) = 165.34 kg/m
○ Now, to calculate
the spacing between the two idlers we will use the eqn.1.1
S=(8*50000*0.015)/(15+165.34)*9.81
= 3.391 m
○ The diameter of the
idler can be calculated from the eqn.1.3 as below:
D=
(60*1.68)/ (3.14*50) = 0.64 m
○ Total load acted on
each idler can be obtained from the eqn.1.4 :
F=(10*1000*3.391*9.81)/(36*1.68)=5500
N
○ Maximum bending
stress applied on each idlers can be obtained from the eqn.1.5 as below:
b=
(8*5500*1.2)/ (3*3.14*0.643) = 21385.176 N/m2
If the
maximum bending stress calculated from the above equations is higher than the
accepted limit of the bending stress then, you have to reconsider the input
assumed parameters, for example you may have to set the lower idler speed or
you have to think of the lower belt sag value, so that idler spacing got
reduced and so the load per idler.
Conclusion
There are
three types of idlers used in the conveyor industry, out of which only the flat
belt conveyor idler design calculations are discussed here theoretically. We
have not used the factor of safety in the design calculations here, or in other
words the factor of safety is considered as one throughout the calculations.
The theoretical calculations are ideal for the preliminary design. FEA
tools like Ansys or Pro Mechanica should
be used for the final virtual validation of the design.