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Torque & Horsepower
Torque and Horsepower Equivalents
TORQUE: A turning moment or twisting effort that can be expressed in foot-pounds
A foot-pound is the amount of energy expended
in lifting a one-pound mass a distance of one
foot against the pull of gravity.
FOOT-POUNDS INDICATES ENERGY
A pound-foot is the movement created
by a force of one pound applied to the
end of a lever arm one foot long
POUND-FEET INDICATES TORQUE
Torque (in Pound-Inches) = 63,025 x HP / RPM
= Force x Lever Arm (in inches)
Torque (in Pound-Feet) = 5,252 x HP / RPM
= Force x Lever Arm (in Feet)
Force = Working Load in Pounds
FPM = Feet Per Minute
RPM = Revolutions Per Minute
Lever Arm = Distance from the Force to the center or rotation
in Inches or Feet.
25 HP at 150 RPM = 875 Pound-Feet Torque
2.5 HP at 150 RPM = 1050.4 Pound-Inches Torque
A common unit of mechanical power. One HP is the rate of
work required to raise 33,000 pounds one foot in one minute.
HP = Force x FPM / 33,000
HP = Torque (in Pound-Inches) x RPM / 63,025
HP = Torque (in Pound-Feet) x RPM / 5,252
A bending force imposed on a shaft due to the torque
transmitted by V-drives, chain drives and other power transmission devices, other
than flexible couplings.
Most motor and reducer manufacturers list the maximum values allowable for overhung
loads. It is desirable that these figures be compared with the load actually imposed by
the connected drive.
O.H.L. = 63,000 x HP x F / N x R
HP = Transmitted HP x service factor
N = RPM of shaft
R = Radius of sprocket, pulley, etc.
F = Factor
1.00 for single chain drives
1.10 for Timing belt drives
F= 1.25 for spur or helical gear
1.25 for double chain drives
1.50 for V-belt drives
2.50 for flat belt drives
Weights of the drive components are usually negligible. The formula is based on the assumption that the load is
applied at appoint equal to one shaft diameter from the bearing face. Factor F depends on the type of drive used.
EXAMPLE: Find the over hung load imposed on a reducer by a double chain drive transmission 7 HP @ 30 RPM.
The pitch diameter of the sprockets is 10’’, service factor is 1.3.
O.H.L. = (63,000) (7 x 1.3) (1.25) / 30 x 5
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