User guide

product
application guide
®
A technical bulletin for engineers, contractors and students in the air movement and control industry.
Fan Application
FA/103-00
P.O. Box 410 • Schofield, WI 54476 • 715.359.6171 • Fax [phone]
®
Copyright © 2000 Greenheck Fan Corp.
Understanding bearings for the fan industry
Bearings are one of the most critical components in
the operation of a fan and careful consideration
must be given to the selection of the appropriate
bearing for each application. Fan manufacturers
that have comprehensive product line ranging from
small light duty commercial fans to heavy duty,
high-speed
industrial
fans
inherently
acquire more
experience in
bearing
application.
Through the
years
Greenheck
has worked closely with our bearing supplier
partners to establish the quality features required
for our full range of products, and to provide the
bearing life expectancy required by our industry.
The following information is intended as a guide to
understand fan-bearing life, components and some
of the typical applications for which they are used.
We will begin our discussion by defining some of
the industry terms used to describe bearing life
expectancy.
Bearing Life
Bearing life is usually expressed as the number of
hours an individual bearing will operate before the
first evidence of metal fatigue develops in the rings
or rolling elements. In past years, four different
terms were used when referring to bearing life. The
terms commonly used were B
10
or L
10
and B
50
or
L
50
. The terms B
10
and L
10
had the same meaning
and the terms B
50
and L
50
also had the same
meaning. It’s time to end the confusion! In today’s
terminology the preferred term is L
10
. However, L
50
is sometimes used, therefore both meanings must
be understood.
L
10
life: The preferred term in specifying bearing life.
The American Bearing Manufacturers Association
(ABMA), formerly the AFBMA defines the Basic
Rating Life, L
10
as the bearing life associated with a
90% reliability when operating under conventional
conditions, i.e. after a stated amount of time 90% of
a group of identical bearings will not yet have
developed metal fatigue. L
10
life is also referred to
by manufacturers as the `minimum expected life’.
L
50
life: Or average life.
Although the L
10
life is the proper method of
specifying fatigue life per the ABMA, another term
is often used in the industry. The L
50
or average life
is accepted as the bearing life associated with a 50%
reliability, i.e., after a stated amount of time, only
50% of a group of identical bearings will not yet
have developed metal fatigue. L
50
life equals five
times the L
10
life.
In other words, to get a L
50
life equal to a L
10
80,000-hour life, you must specify the L
50
life to be
400,000 hours. The following chart shows a
comparison of L
10
to L
50
equivalents.
Required L
10
Equivalent L
50
(avg)
Life Hours Life Hours
20,000 100,000
40,000 200,000
80,000 400,000
100,000 500,000
200,000 1,000,000