Greenheck FA/103-00 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 B10 or L10 and B50 or
L50. The terms B10 and L10 had the same meaning
and the terms B50 and L50 also had the same
meaning. It’s time to end the confusion! In today’s
terminology the preferred term is L10. However, L50
is sometimes used, therefore both meanings must
be understood.
L10 life: The preferred term in specifying bearing life.
The American Bearing Manufacturers Association
(ABMA), formerly the AFBMA defines the Basic
Rating Life, L10 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. L10 life is also referred to
by manufacturers as the `minimum expected life’.
L50 life: Or average life.
Although the L10 life is the proper method of
specifying fatigue life per the ABMA, another term
is often used in the industry. The L50 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. L50 life equals five
times the L10 life.
In other words, to get a L50 life equal to a L10
80,000-hour life, you must specify the L50 life to be
400,000 hours. The following chart shows a
comparison of L10 to L50 equivalents.
Required L10 Equivalent L50 (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

Greenheck Product Application Guide
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Fan Application No. FA/103-00
Writing the Bearing Specification
Basic Rating Life, L10 is a useful tool when
specifying a given level of bearing construction.
When required to provide a given L10 life, all
equipment manufacturers must supply the same
capacity bearing for a given RPM and shaft
diameter. Also, an 80,000 hour L10 bearing will have
a theoretical life twice as long as a 40,000 hour L10
bearing and hence will last longer in the field.
Here’s Greenheck’s recommendation for a typical
bearing specification:
“Bearings shall be air handling quality, heavy duty
grease lubricated, ball or roller type. Bearings shall
be selected for a Basic Rating Life, (L10) of 80,000
hours at maximum operating speed and
horsepower for each construction level.” (Air
handling quality means the bearings meet the
requirements for use in air handling applications; high
speeds, long life and quiet operation. All bearings are
100% tested for excessive noise levels and bore
dimensions are verified to be within tolerances.)
Note: If all the fan products you are specifying are
from the Greenheck Fan & Vent catalog, you can
specify L10 100,000 hour life bearings at no extra
charge.
The chart below provides another way to look at
the expected bearing life. Assuming you specified
Greenheck’s standard bearing life of L10 80,000
hours and your fans run an average of 8 hours per
day, you can expect 27.5 years of life on 90 percent
of the bearings.
In most cases, the Basic Rating Life will be much
greater than shown because the bearings are
selected for the maximum RPM and horsepower for
each size and fan class. Most fans are selected
significantly below their maximum fan rpm.
*Bearings with a L10 200,000 hour life are optional
for most centrifugal and vane axial products.
However, in most cases, it is not practical to specify
L10 200,000 because of the associated cost. (And, do
you really need the bearings to last for 68 years?) It
is more practical for your customer to spend the
additional money on maintenance.
Avoid writing bearings specifications without
having the correct Basic Rating Life (L10 or L50)
terms in front of the required hours of life. If your
specification reads 200,000 hour bearing life, your
chance of getting what you want is minimal. Some
suppliers will assume L50 200,000 life is all that’s
required and you will end up with an inferior
bearing system. Other suppliers will assume you
are specifying the optional L10 200,000 hour life and
add unnecessary cost. The best suppliers will ask
for a confirmation of the L10 life required.
No Guarantee
Bearing Basic Rating Life is theoretical and is based
on a collection of statistics. Specifying a L10 life
does not guarantee that the fan bearings will have a
90% reliability when installed on a fan in the real
world. The calculation for Basic Rating Life
assumes proper lubrication is provided, no shock or
vibration exists, alignment is virtually perfect, no
debris enters the bearings and ambient
temperatures are not extreme. In the real world,
none of these conditions are realistic and the
“installed life” of the bearing will depend on the
application and maintenance.
To get as close as possible to the specified life, the
installer and end user must follow the
recommendations in the manufacturer’s installation
and maintenance instructions. Once the bearing life
expectancy is clearly defined, that information can
then be combined with other bearing requirements
to select the most appropriate bearing for each
application.
Bearing selection
Most manufacturers use some type of bearing
selection program that calculates equivalent bearing
loads and bearing life. Some of the main selection
criteria include shaft diameter and weight; lubricant
viscosity; motor horsepower; fan sheave pitch
diameter, weight and location on the shaft; fan
speed; fan wheel weight; bearing and wheel
L10 Life Average running hours per day
81624
80,000 27.5 yrs 13.7 yrs 9.2 yrs
100,000 34.3 yrs 17.2 yrs 11.4 yrs
200,000* 68.6 yrs 34.3 yrs 22.8 yrs
*Years of bearing life for fans running seven days a week,
fifty two weeks per year.

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Fan Application No. FA/103-00
Greenheck Product Application Guide
locations on the shaft; thrust loads; and the
direction of belt pull. Most often the selection
program used is one developed by a bearing
manufacturer. Greenheck engineers use Dodge
bearing selection software. Based on the output
results of this data, Greenheck engineers are able to
select the bearings that best meet each individual
application.
Light duty bearings
Ball bearings with stamped steel housings are well
suited for applications with very light loads and
lower speeds. The main design characteristic that
defines stamped
bearings is the rubber
sleeve around the
bearing insert, which
snaps into the
stamped housing. The
use of these bearings
is limited to fan
products with 3⁄4 inch
and smaller diameter
shafts, and one
horsepower and smaller motors.
Air handling quality
When the operating level of the ball bearings with
stamped steel housing is exceeded, air handling
quality ball, spherical or tapered roller pillow block
or flange-mount bearings are primarily specified.
These bearings have been engineered specifically
for air handling applications and feature special
construction and tighter quality control. In order for
a bearing to be of “air handling quality,” it must
meet the following specifications:
1. Reduced swivel torque
Proper alignment of the bearing to the shaft is
essential in preventing vibration, noise and damage
to the bearing components. To allow a bearing to
self align under light loading, it must have a low
swivel torque. A low swivel torque enables the
outer race of the bearing to pivot or swivel within
the cast pillow block, allowing the bearing to align
to the shaft much easier. It should be noted that this
feature is special only to air handling ball bearings
and tapered roller bearings. Spherical designs
inherently allow for easy self-aligning because the
race has a radius that allows the rollers to pivot
somewhat within the race, so the race doesn’t need
to pivot within the pillow block.
2. Noise and vibration testing
All “air handling quality” bearings are 100%
vibration tested. These high test standards are
designed to discover microscopic manufacturing
defects that may either cause higher noise levels or
lead to premature failure of the bearing.
3. Bore Size Test
All “air handling quality” bearings are 100%
inspected to insure that the inner race diameter is
within tolerance. A bore size larger than tolerance
would allow the bearing to shift which could cause
misalignment.
The benefits of “air handling quality” bearings to
the life of ventilation equipment are being seen
throughout the HVAC industry. More and more
manufacturers are providing air handling quality
bearings as their standard.
Ball bearings
The Dodge D-Lok pillow block bearing
incorporates a “heavy-clamp-style” locking collar as
an alternative to the typical set screw locking
system. This design allows the bearing race to be
tightened concentrically about the shaft. This type
of locking mechanism gives two distinct advantages
over the set screw method. First it maintains one
common center axis of the shaft and bearing,
whereas tightening of the set screw forces the shaft
off to one side, offsetting its rotating axis. Secondly,
the shaft and bearing race come into surface-to-
surface contact upon tightening. This increase in
contact surface area not only improves the holding
strength of the bearing to the shaft, but it also
eliminates problems with burring on the shaft
caused by the tightening of set screws.
Application
Greenheck uses Dodge
D-Lok ball bearings for
all centrifugal, vane
axial and industrial
units within the ball
bearing application
range. In our fan and
ventilation line, Dodge
D-Lok ball bearings are
Ball Bearing with rubber sleeve
and stamped steel housing.
Ball bearing with D-Lok

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Fan Application No. FA/103-00
used on Greenheck’s extended pressure CUBE
exhaust fans (Model Cube-XP).
The balance of the fan and ventilator products that
exceed the limitations of the
stamped steel bearings use the
air handling ball bearing with
the set screw locking method.
This includes fans with a shaft
diameter of one inch and
larger, and a motor of 1 1⁄2
horsepower and larger. In
applications with lower speeds
the D-Lok mechanism is
available, however, the D-Lok
advantages are negligible and
not cost justified.
When the application load and speed exceed the
capacity of ball bearings, roller pillow block
bearings are typically
specified. Like ball
bearings, roller bearings
can carry a combination
of radial and thrust loads;
however, roller bearings,
in order to operate
properly, require a radial
load at least equal to the
thrust load. Insufficient
radial loading allows the rollers to skid within the
race, which could cause premature failure of the
bearing components. Tapered roller bearings that
are similar to the spherical rollers, are commonly
specified for vertical applications where high thrust
loads are encountered.
Currently, roller bearings are available with either
the standard set screw-locking method, or the
Dodge Imperial patented adapter-mounting system
(spherical roller bearings only).
Thus far all of the bearing options we have
discussed have been in a solid housing, either
stamped or pillow block. Once the application
exceeds the speed limit for the contact seal and
grease sump design of the solid housing, a split
pillow block bearing is typically specified. The split
pillow block design incorporates a friction-free
labyrinth seal and a larger grease cavity. Higher
speeds can then be attained and the rollers become
the limiting factor instead of the seal.
Split pillow block housings incorporate a tapered
adapter sleeve-mount locking
system. Because of the
geometry of the sleeve-mount
design, a larger bearing is
required for the same shaft
size as would be used in a
solid pillow block design.
Consequently, the capacity of
the rollers increases, thus
requiring a higher minimal radial load for proper
operation of the rollers.
In some applications where contaminants need to
be kept out of the bearing, special seals other than
the labyrinth-type are used in the split pillow block
housing. In these cases, the seal may be a speed-
limiting factor and must be accounted for in the
selection of the bearing.
In certain products, such as some vane axial belt
drive fans, the installation of a pillow block bearing
can be difficult simply because of physical space
constraints within the belt
tube. In such a case, a flange-
mount bearing can be used.
The bearing components are
essentially the same as the
pillow block version, but the
housing allows for face
mounting around the shaft
instead of pedestal mounting
under the shaft.
Summary
The information in this article is a guideline to help
communicate a better overall understanding of
bearings and good bearing application.
Don’t let your air handling equipment suffer a short
life span because of premature bearing failure.
Applications are often times unique, and your
selection will be based upon the bearing options
best suited to your job specifications.
Greenheck engineers have over 40 years of
experience in bearing selection and work closely
with our vendors to ensure customers receive the
highest quality products. Determine what bearing
life your application requires and let Greenheck’s
experienced engineering team specify the right
bearing for the job.
Roller bearing with set screw
Ball bearing with set
screw
Flange mount bearing
Split housing