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Drive Belts


Flat Belt Drives

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
  1. Pulleys need to be crowned to prevent belt from wandering off. Belts tend to move to tightest position
  2. Tension required to enable belt to operate. Tensions normally set by adjusting centre distance between pulleys to ensure some stretch of belts (say 2%).
  3. 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
LubricationCoefficient
of Friction (μ)
Leather on WoodLubricated0,47
Leather on Cast IronGood Lubrication0,12
Leather on Cast IronLow Lubrication0,38
Steel Band on Cast Iron Dry0,18


Links to Belt Design
  1. Components for Drivelines- Flat Belts..Short informative article
  2. Forbo-Siegling ..Flat Belt Manufacturer- Site includes useful information


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Last Updated 20/01/2013