Belts - Length and Speed of Belt
Length and speed of belt, belt gearing
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Belts are used to transfer power through rotational motion from one shaft to an other. Belt driven fans are common in heating, ventilation and cooling systems.
- friction belts - transfer power through friction between the pulley and the belt
- synchronous belts - transfer power through mechanical linkage between the teeth in the belt and grooves in the pulley
Belt Length
The length of the belt can be calculated as
lb = ((df + dm) 1.5708 ) + (2 lfm) ? (1)
where
lb = length of belt (mm, inches)
df = pulley (sheave) diameter fan (mm, inches)
dm = pulley (sheave) diameter motor (mm, inches)
lfm = center to center distance of fan and motor pulleys (mm, inches)
Belt Velocity
The velocity at which a belt travels may be expressed as
v = π dm nm / 12 (2)
where
v = velocity of belt (ft/min)
nm = velocity motor (rpm)
Belt Gearing
The relationship between the speed of the motor, the fan and their disc diameters can be expressed as
df? nf = dm nm (3)
Horsepower
If belt tension and belt velocity are known - horsepower transferred can be calculated as
Php = T v / 33000 (4)
where
Php = power (hp)
T = belt tension (lbf)
v = velocity of belt (ft/min)
If torque and revolution per minute are known - horsepower transferred can be calculated as
Php = M R / 63000 (4)
where
Php = power (hp)
M = torque (lbf)
R = revolutions per minute (rpm)
Speed Ratio
Speed ratio can be calculated as
SR = Rf / Rs (5)
where
SR = speed ratio
Rf = revolutions per minute - fastest machine
Rs = revolutions per minute - slowest machine
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