Conveyor Design Steps:
- Establish
conveying requirements
- Identify
the material and the corresponding material code
- Determine
conveying capacity, conveyor size and speed
- Calculate
required horsepower — select motor size
- Determine
the recommended size of components
- Check
the torsional ratings of components
- Check
deflection, thermal expansion and abrasion
Step 1: Establish conveying
requirements
To properly design a conveyor to meet
your needs it is important to know several parameters surrounding the
application. Fortunately, to begin, you only need to know a few. These are:
• Type of material to be conveyed
• Required flow (lbs per hour or cubic
feet per hour)
• Distance material will be conveyed
Step 2: Identify material and
corresponding material code
The type of material being moved can
have a significant affect on the size and type of conveyor needed. The
following charts will help you classify your material and will help in
selecting the proper conveyor components.
You can easily find out code of
material using table A and table B
Step 3: Determine conveying
capacity, conveyor size and speed
For screws
with standard, full pitch flights the conveyor’s speed is:
N = screw
rpm (not greater than the max recommended speed)
For the calculation of conveyor speeds where special types of screws are
used, such as short pitch, cut flights, cut and folded flights and/ or ribbon
flights, an equivalent required capacity must be used, based on factors in Table
C. The equivalent capacity then is found by multiplying the required capacity
by one or more of the capacity factors that are involved.
Equivalent Capacity (ft3/hr) =
Required Capacity x CF1 x CF2 x CF3
In this case:
L= Length of
screw conveyor in ft.
Step 4: Calculating Horsepower
(Horizontal Conveying)
The horsepower required to operate a horizontal
screw conveyor is based on proper installation, uniform and regular feed rate
to the conveyor and other design criteria. The horsepower requirement is the
total of the horsepower to overcome the friction (HPf) of the
conveyor components and the horsepower to transport the material
(HPm) multiplied by the overload
factor (Fo) and divided by the total drive efficiency (e), or:
The following factors determine the horsepower
requirement of a screw conveyor operating under these conditions.
L
|
=
|
Total length of conveyor, feet
|
N
|
=
|
Operating speed, rpm
|
C
|
=
|
Capacity required, cubic feet per hour
|
D
|
=
|
Density of material as conveyed*, lb/CF (See Table B)
|
Fd
|
=
|
Conveyor diameter HP factor (See Table
L)
|
Fb
|
=
|
Hanger bearing HP factor (See Table
M)
|
Fm
|
=
|
Material factor (See Table B)
|
Ff
|
=
|
Flighting modification HP factor (See Table J)
|
Fp
|
=
|
Paddle HP factor (See Table K)
|
Fo
|
=
|
Overload HP factor (See Table H)
|
e
|
=
|
Drive effic. (expressed as a decimal) (See Table G1) |
It is generally accepted practice that most power transmitting elements of a screw conveyor be sized and selected to safely handle the rated motor horsepower. If, for example, a screw conveyor requires 3.5 horsepower as determined by the above formula, a 5 horsepower motor must be used and it is desirable that all the power transmitting elements be capable of safely handling the full 5 horsepower.
*Some materials, such as cement, will aerate
when conveyed making their apparent density much lower than when static. This
is factored into the densities shown in Table
B.
