Introduction
In many factories in the past flat belts have been widely used to drive the machines
in the factories. They are convenient to install and operate and are reliable. In modern times
machines are driven individually generally using electric or hydraulic drives...
Flat belt drives are now mostly used for low power high speed applications in specialised
industries including the textile, paper making, and in office machinery.
Flat belts are
also used for conveyor applications.
Practical Notes
- Pulleys need to be crowned to prevent belt from wandering off. Belts tend to move to
tightest position
- Tension required to enable belt to operate. Tensions normally set by adjusting centre
distance between pulleys to ensure some stretch of belts (say 2%).
- Best drives result from belts with high flexibility, low mass, and with surfaces
engineered to provide a high coefficient of friction
|
Flat belt designs
In the past belts were generally made from leather. Now belts are also manufactured
from a wide range of elastomer including urethane, neoprene,
hypalon, EPDM, and silicone. Stretch, semi-stretch, and no-stretch belts
are available. Belts are often reinforced with textiles and fibres and
and metal reinforced belts are available. Belts can be provided with durable
surface coatings and coatings providing anti-static properties
Service Factors
When designing belt drives it is normal to apply a service factor to the drive operating
load to compensate for allow for different driver type, driven load types and operating
periods. Typical ervice factor values are included on the linked page Service Factors
Basic Theory
Fc = Centrifugal Force (N)
R = Pulley reaction Force (N)
P = Max power transferred kW
T = Belt tension
Tc = Belt tension due to centrifugal force
μ = Coefficient of Friction.
b = Belt width (m)
ω = Angular velocity of pulley (rad/s)
n = Rotational Speed (RPM)
θ = Angle of belt lap
v = Linear velocity of belt (m/s)
|
Note: If two pulleys of different diameters are used then in driving to the limit
the belt will slip on the smaller pulley first
Power transferred by a flat belt
The power transferred =
P = (T1 - T2 ).v / 1000
= (T1 - Tc) - (T2 - T c ).v / 1000
= (T1 - T2 ) (1 - e-μθ ).v /1000
Belt Friction Factors
Material
Combination | Lubrication | Coefficient
of Friction (μ) |
| Leather on Wood | Lubricated | 0,47 |
| Leather on Cast Iron | Good Lubrication | 0,12 |
| Leather on Cast Iron | Low Lubrication | 0,38 |
| Steel Band on Cast Iron | Dry | 0,18 |
|
