Fan Application
FA/103-00
®
product
application guide
A technical bulletin for engineers, contractors and students in the air movement and control industry.
Understanding bearings for the fan industry
Bearings are one of the most critical components in
meaning. It’s time to end the confusion! In today’s
the operation of a fan and careful consideration
must be given to the selection of the appropriate
bearing for each application. Fan manufacturers
terminology the preferred term is L . However, L
is sometimes used, therefore both meanings must
be understood.
10
50
that have comprehensive product line ranging from
small light duty commercial fans to heavy duty,
L
life: The preferred term in specifying bearing life.
10
high-speed
industrial
fans
inherently
acquire more
experience in
bearing
application.
The American Bearing Manufacturers Association
(ABMA), formerly the AFBMA defines the Basic
Rating Life, L as the bearing life associated with a
10
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 life is also referred to
10
by manufacturers as the `minimum expected life’.
Through the
years
L
life: Or average life.
50
Greenheck
Although the L life is the proper method of
specifying fatigue life per the ABMA, another term
10
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.
is often used in the industry. The L or average life
50
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
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.
have developed metal fatigue. L life equals five
50
times the L life.
10
In other words, to get a L life equal to a L
50
10
80,000-hour life, you must specify the L life to be
50
400,000 hours. The following chart shows a
comparison of L to L equivalents.
10
50
Bearing Life
Required L
Equivalent L (avg)
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
10
50
Life Hours
Life Hours
20,000
40,000
80,000
100,000
200,000
100,000
200,000
400,000
500,000
1,000,000
terms commonly used were B or L and B or
10
10
50
L . The terms B and L had the same meaning
50
10
10
and the terms B and L also had the same
50
50
®
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Copyright © 2000 Greenheck Fan Corp.
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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.
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.
Light duty bearings
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.
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
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 Bearing with rubber sleeve
and stamped steel housing.
Ball bearings
The Dodge D-Lok pillow block bearing
shafts, and one
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.
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
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 D-Lok
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3
Fan Application No. FA/103-00
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Greenheck Product Application Guide
used on Greenheck’s extended pressure CUBE
exhaust fans (Model Cube-XP).
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
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
Split housing
requiring a higher minimal radial load for proper
operation of the rollers.
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.
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.
Ball bearing with set
screw
When the application load and speed exceed the
capacity of ball bearings, roller pillow block
bearings are typically
specified. Like ball
bearings, roller bearings
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
can carry a combination
of radial and thrust loads;
however, roller bearings,
tube. In such a case, a flange-
mount bearing can be used.
The bearing components are
in order to operate
properly, require a radial
load at least equal to the
essentially the same as the
pillow block version, but the
housing allows for face
Roller bearing with set screw
thrust load. Insufficient
mounting around the shaft
instead of pedestal mounting
under the shaft.
Flange mount bearing
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.
Summary
The information in this article is a guideline to help
communicate a better overall understanding of
bearings and good bearing application.
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).
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.
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.
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.
Split pillow block housings incorporate a tapered
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Fan Application No. FA/103-00
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