Tension … According to “Belt Wizard”
Conveyor operating “tension” is a fundamental criterion for belt selection. Over the years, many
formulation methods have been created and utilized for making such calculations.
Most of us are familiar with FDA’s “Belt Wizard” computer program. This customized program,
based on the “CEMA model,” is a unique blending of
various empirical formulas and field/operational data.
Over the years, these formulations have been
continually refined and updated … making “Belt
Wizard” one of the most sophisticated and successful
steady-state tension models available today.
“Belt Wizard” makes all its calculations … including
tension … from the input of a wide range of possible
operational and product data. In the days before the
“computer age,” such complex tension calculations
could be very time-consuming! Back then, we referred
to any of these more detailed tension models as the
“long” calculation method.
“Full-Motor” Calculation … an Alternative
To save time in those pre-digital days, we often opted
to calculate tension using the “Full-Motor” method!
This alternative tension approach had some obvious
advantages … among them, requiring only a few basic
inputs, and just ONE simple calculation! It also had
some limitations … most noted was an “inflated”
tension value. Sometimes referred to as the “short”
tension calculation method, the “Full-Motor”
calculation was typically represented as follows:
… where: … and, Cw = drive “wrap factor”
PIW = lbs/in width (max operating tension) Wrap Automatic TU Manual TU
S = belt speed (ft/min) Bare Lagge Bare Lagge
W = belt width (inches) d d
HP = motor horsepower (nameplate) 1800 0.84 0.50 1.2 0.8
210 0.66 0.38 1.0 0.7
“Full-Motor” Tension Realities:
Basic Assumption … This simple tension format is based on assuming that 100% of the
motor’s nameplate horsepower will be delivered directly into the belt.
That, of course, can never happen!! Actual belt tension…as calculated by any more
detailed “long” method…will surely reflect some lesser value.
Such maximum tension calculations should only be used as an “initial estimate.” (Final
belt selection still needs to be qualified by the other four carcass selection criterion.)
Horsepower/Speed Relationships …
Horsepower and speed are critical
inputs to the “Full-Motor” calculation.
When motor nameplate values exceed
75 hp, and/or belt speeds drop below
300 feet/min, the calculated tension
values can become unreasonably high.
In such situations, I seldom would even
bother with this calculation formula!!
Cw (or Drive “Wrap Factor”) …
This input data is based on drive wrap
angle, lagging, and takeup information.
From these inputs, several “wrap … Checking belt “speed”
factor” combinations are indeed
possible. On the previous page, I
merely charted the Cw combinations that tended to be more common with lower motor
horsepower applications. (For a more complete listing of “wrap factor” combinations, refer to
p. 133 of the CEMA v6 manual.)
In spite of today’s sophistication and availability of computer programs like “Belt Wizard,” I’ll still
find myself using this “Full-Motor” calculation method … and often on a daily basis!
True, using it will ALWAYS
generate HIGH tension values!
Yet, in many applications, or field
issues, belt tension is simply not a
factor! Sometimes, I may not even
be in a position to access my “Belt
Wizard” program (traveling, etc).
In these instances, that simple
“Full-Motor” calculation will
quickly help to “guide me”
through the belt selection or the … “Full-Motor” candidates!!
field problem-solving process.
If you’re not already familiar with the “Full-Motor” calculation routine, you might want to get
acquainted with it. I’m betting that it can help assist you in a similar fashion!
George “Big G” Frank
Manager, Application Engineering