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SS S S C C C C C R R R R R E E E E E P P P P P O O O O O R R R R R T T T T T Status of Bearing Load Ratings
Status of Bearing Load Ratings
Status of Bearing Load Ratings
Status of Bearing Load Ratings
Status of Bearing Load Ratings
Volume 2, Issue 2
August 15, 1990
Copyright 1990 by BSA
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BSA Educational Services Committee
Raymond Brocato,
Chairman
Bert Robins
James Detzel
Charles Martin
Fred Mohr
Charles Nicholson
Alex Toback
James Abercrombie
William Botterill
Michael Messer
James Fitzpatrick, Jr.
The ESC Report is a program of the Educational Services Committee intended to keep
members informed about topics affecting the bearings industry. Comments may be sent to the
committee c/o BSA, 800 Roosevelt Road, Building C, Suite 20, Glen Ellyn, IL 60137-5833.
www.bsahome.org; e-mail: info@bsahome.org.
Until recently, bearing manufacturers used a standard method of
calculating the static and dynamic load ratings. These standard methods
were developed in the late ’40s and early ’50s and were recognized by the
International Standards Organization (ISO) and American National
Standards Institute (ANSI)/Anti-Friction Bearing Manufacturers
Association (AFBMA). The use of these standard methods resulted in a
straightforward method for the user to compare bearings.
This all changed during the ’60s. Bearing manufacturers realized that
since the early 1950s, significant improvements in bearing performance
had been achieved, the most important of which were cleaner bearing
steels and improved understanding/control of bearing geometry. Although
the standards used for calculating the ratings needed to be updated, which
would take some time, bearing manufacturers attempted to show this
improved performance in their catalogs. Unfortunately, they used different
procedures to show these improvements.
Two basic methods were used to show the improved performance of the
bearings. The first was to use the original load rating and indicate that life
had improved, either in time or revolutions. Bearings were shown to last
up to three times longer than before.
The other method of showing the improvement in bearing performance
was to increase the load rating for the original life. The improvements in
load ratings were up to 1.42 times the original values.
With these two very different methods, it was difficult and sometimes
impossible to determine if like bearings had similar performance
characteristics.
The ISO and AFBMA have been working for the past several years to
update these standards, and it now appears that they will complete their
work in the near future. The ISO and AFBMA standards are very similar,
although there are some exceptions (which will be covered later). The ISO
and AFBMA used the method of increasing the load ratings to show
improved bearing performance. The standards are listed below.
Page 1
® ISOISO 76 Static Load Ratings
ISO 281 Dynamic Load Ratings
ANSI/AFBMA
Std. 9
Ball Bearing Load Ratings
Std. 11 Roller Bearing Load Ratings
The improvement factors for dynamic
load ratings in these updated standards
are shown below. An improvement factor
of 1.0 indicates the rating is the same as
the original value.
The only difference between the ISO
and AFBMA standards is the
improvement factor for insert bearings,
which is still in the process of being
resolved. There will probably be an effort
to make the improvement factor for
Page 2
Bearing Type
Ball Bearings
Single row radial contact
groove ball bearings and
single and double row
angular contact groove
ball bearings
Insert ball bearings
Filling slot ball bearings
Double row radial contact
groove ball bearings
Single and double row self-
aligning ball bearings
Single row radial contact
separable ball bearings
(magento bearings)
Thrust ball bearings
Roller Bearings
Cylindrical roller bearings,
tapered roller bearings and
needle roller bearings with
machined rings
Drawn cup needle bearings
Spherical roller bearings
ISO
1.3
1.0
1.1
1.3
1.3
1.3
1.3
1.1
1.0
1.15
AFBMA
1.3
1.3
1.1
1.3
1.3
1.3
1.3
1.1
1.0
1.15
Improvement
Factor
D
YNAMIC
L
OAD
R
ATINGS
tapered roller bearings the same as the
spherical roller bearings.
Because they are now based on the
maximum contact stress that a bearing can
endure before significant permanent
damage occurs, static load ratings for ball
bearings have been increased. These load
ratings used to be based on the allowable
permanent deformation. This new method
lends itself to a more simple method of
calculating the values. Only the ball bearing
was changed based on the determination
that ball bearings can handle a greater
contact stress than roller bearings before
significant permanent damage occurs. The
ISO and AFBMA improvement factors for
static load ratings are the same and are
shown below.
The development of these standards is a
significant step toward correcting the load-
rating situation. The next phase of this
effort will be the updating of the
manufacturers’ catalogs. It is not clear
whether all manufacturers will update their
catalogs to agree with these new standards;
even if they do, it will take a long time and
out-of-date catalogs will still exist.
For this reason, bearing users will be
faced with this problem for some time. In
the meantime, we would recommend that
the user specify load ratings based on the
ISO and AFBMA standards.
Radial and angular
contact groove ball
bearings
Self-aligning ball bearings
Thrust ball bearings
Roller bearings
S
TATIC
L
OAD
R
ATINGS
Bearing Type
Improvement
Factor
1.15
1.50
1.15
1.00