ENGINEERING MANUAL - Design Steps

Step 4 - Calculating Horsepower

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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 cirteria. The following factors determine the horsepower requirement of a screw conveyor operating under these conditions.
Dc = Design capacity in cubic feet per hour
e = Drive efficiency ( as a decimal  Table G)
Fb = Hanger bearing factor ( Table K )
Fd = Conveyor diameter factor ( Table J )
Fm = Material Factor ( Table B )
Fo = Overload Factor ( Table L )
L = Total Length of Conveyor
N = Operating Speed in rpm
W = Weight of material conveyed in lbs/ft3

The horsepower requirements 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:

           L N Fd Fb                                  Dc L W Fm                                     (HPf + HPm) Fo
HPf  = -----------------                 HPm  =  -----------------------              HPtotal  =   -------------------------
           1,000,000                                   1,000,000                                                  e

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.