Much of the world estimates the main resistances with a single overall friction factor,
based on history, though each of the main resistances is affected differently by the
specific material, design and construction details. The Conveyor Equipment
Manufacturers Association (CEMA) has long recognized the individual impact of various
parts and configurations and include a set of power prediction equations addressing
each in its “Belt Conveyors for Bulk Materials,” especially in the sixth edition in 2005 and
the seventh edition. This design and analysis approach has proven to provide a better
foundation for design accuracy and optimization for complex conveyors, especially since
computers have allowed the many calculations and checks needed for thorough design
over a wide range of cooperating conditions.
The main friction losses and their relative contributions as percentage of total power on
a flat conveyor are:
1. Belt rubber indentation rolling resistance from the belt internal hysteresis. It is affected
by load, temperature and compounding of the durable, filled rubbers used on conveyors
(25% to 80%).
2. Idler alignment from imperfect angular alignment during installation and manufacturing
(10% to 50%).
3. Idler rotating resistance from the design and manufacture including seal and
temperature sensitive grease drag (10% to 60%).
4. Bulk material friction due to internal movement from belt sag between each pair of
idlers, especially with belts with fabric carcasses and at lower tension (1% to 55%).
In addition, miscellaneous component can contribute from 2% to 10%. Inclines or
declines dominate the power loss categories and belt tension when the slope is much
greater than 5°, but the above still have an absolute effect on power.
