Ball Bearings for Units

Ball Bearings for Units
Table of Contents
Introduction ……………………….…………….………………………… 2
Ball Bearings ………………………………………………………………. 9
Roller Bearings ……………………………………………………..…….. 17
Rolling element linear bearings ………………………………………….. 23
Plain Bearings …………………………………………………….………. 25
Technical Information ……………………………………………………. 27
Bearing Units ………………………………………..……………………. 38
Introduction of KML ……………………………..………………………. 44
Copyright © 2006
KML Bearing USA, Inc.
July 2006
KML Bearing USA Edition TM806 Bearing Training Manual is the initial publication.
The contents of this publication are the copyright of KML Bearing USA, Inc. and may
not be reproduced in part or in entirety in any form without specific written permission
by the copyright owner.
Every effort has been made to insure the accuracy of the information contained in this
publication. KML Bearing USA, Inc. assumes no liability for any errors or omissions.
The listing of products in this publication does not insure product introduction or
current availability.
KML Bearing USA Inc.
Page 1
Bearings are used to reduce friction and wear whenever relative motion exists between two parts.
No bearing is completely without friction and they do wear with use, however, very little friction
is produced when starting and running, and if properly installed and maintained, they can outlast
the life of the driven machine.
There are two types of friction: sliding and rolling
Bearings can be classified as providing sliding or rolling contact.
KML Bearing USA Inc.
Page 2
Sliding contact bearings & rolling contact bearings
Sliding contact bearings are referred to as plain bearings while rolling contact bearings are
often called “anti-friction” bearings (or rolling element bearings)
Bearings that provide sliding contact fall into three general classes:
- radial bearings that support rotating shafts (sleeve bearings);
- thrust bearings that support axial loads on rotating shafts;
- linear bearings that guide moving parts in a straight line.
Rolling element bearings minimize friction by removing any possible sliding between bearing
surfaces and replacing all contacts with rolling interfaces.
KML Bearing USA Inc.
Page 3
Characteristics of plain bearings
• Their resistance to shock and vibration is greater than rolling element bearings.
• The hydrodynamic oil film produced by plain bearings damps vibration, so less noise is
• They are less sensitive to lubricant contamination than rolling element bearings.
Characteristics of rolling element bearings
• The starting friction between mating surfaces is lower and there is little difference between
this and the dynamic friction produced.
• They are internationally standardized, interchangeable and readily obtainable.
• Maintenance, replacement, and inspection are easy because the structure surrounding rolling
element bearings is simple.
• Generally, many rolling element bearings are capable of carrying both radial and axial loads
simultaneously or independently.
• May be used under a wide range of temperatures.
• Bearing rigidity can be improved by preloading.
KML Notes
KML Bearing USA Inc.
Page 4
Bearing Construction and Nomenclature
Rolling element bearings consist of two rings (an inner ring and an outer ring), rolling
elements and a retainer.
The rolling elements are placed between the two rings and are kept equally spaced from each
other by the retainer.
This construction provides the bearings with smooth rolling movement.
KML Bearing USA Inc.
Page 5
Load Orientation – Terminology
There are two basic loads in bearing application.
o Radial loads. Radial loads refer to loads acting perpendicular to the centerline of the shaft;
o Axial or thrust loads. Axial loads is loads acting parallel to the centerline of the shaft;
In most situations, bearings are subjected to combined loads. Combined loads are comprised of
both radial and axial loads acting simultaneously.
Bearings which are chiefly used for radial loads are referred to as radial bearings. They have a
nominal contact angle α 45º.
Thrust bearings refer to bearings which are chiefly used for axial loads. They have a nominal
contact angle α 45º.
KML Bearing USA Inc.
Page 6
Rolling elements
Rolling elements come in two general shapes: balls and rollers
Rollers come in four basic styles: cylindrical, needle, tapered and spherical
Cylindrical roller
Needle roller
Tapered roller
Symmetrical spherical roller
Unsymmetrical Spherical roller
Needle rollers have a much smaller diameter-to-length ratio than cylindrical rollers.The diameter
of needle rollers is usually less than ¼" in diameter. The length of a needle roller can range from
3 to 10 times its diameter.
KML Notes
KML Bearing USA Inc.
Page 7
Classification of rolling bearings
Rolling bearings
Ball bearings
Roller bearings
Radial ball bearings Thrust ball bearings Radial roller bearings Thrust roller bearings
Deep groove ball ball bearings
Angular contact ball bearings
Self-aligning ball bearings
Four point contact ball bearings
Insert ball bearings
Cylindrical roller bearings
Needle roller bearings
Tapered roller bearings
Spherical roller bearings
Cylindrical roller thrust bearing
Needle roller thrust bearings
Tapered roller thrust bearings
Spherical roller thrust bearings
Ball bearings and roller bearings
• Ball bearings exhibit a lower frictional resistance and lower face run-out in rotation than roller
• Ball bearings are more suitable for use in applications which require high speeds, high
precision, low torque and low vibration;
• Since the rolling elements in roller bearings make line contact with raceways, roller bearings
have a larger load carrying capacity that makes them more suitable for applications requiring
long life and endurance for heavy loads and shock loads.
KML Bearing USA Inc.
Page 8
Ball Bearings
Single Row Deep Groove Ball Bearings (SRDG)
Single row deep groove ball bearings are the most commonly used bearings and the most popular
type for all ball bearing applications. Deep groove ball bearings are suitable for high-speed
Somewhat self-aligning, deep groove ball bearings allow a minor misalignment (1/6 degrees)
without affecting the bearing operation and life.
Deep groove ball bearings meet diverse application requirements: open type, prelubricated, with
one or both sides sealed or shielded or with snap rings, etc.
KML bearings construction code:
NR: with snap ring
ZZ: with double shields
2RS: with double non-contact seals
2RD: with double light contact seals
2RK: with double contact seals
These are sometimes called Conrad bearings. They are assembled by offsetting eccentrically the
inner and outer rings to allow the insertion of balls (see figure above). The Conrad bearings
therefore have uninterrupted ringways (no filling slot) which permits excellent bearing
performance under light to moderate radial loads, relatively moderate axial loads, or combined
radial and axial loads.
KML also has cartridge type deep groove ball bearings which have the same standard bore and
O.D. as single row deep groove ball bearings, but are as wide as double row ball bearings. They
are supplied with two seals or shields and contain a large grease capacity found useful in
extremely dirty and dusty conditions.
KML Bearing USA Inc.
Page 9
Bearings: Sealed and Shielded
Sealed Bearings
The construction of these bearings is shown below. It has a flexible nonmetallic member secured
to the outer ring and makes a light contact on the inner ring.
1. Entry of contaminants is less likely than open bearings.
2. No regular relubrication is necessary nor possible.
The bearing life is restricted to the lubrication packed between the seals of the bearings.
Sizes available are restricted due to the excessive heating on larger sizes.
Maintenance requires replacement of the bearings.
Higher Friction Losses.
KML Bearing USA Inc.
Page 10
Shielded Bearings
Shielded bearings are also a variation of the Conrad bearings and are very similar to the sealed
type bearings except that the shielded bearings have metallic rather than non-metallic shields.
The metal member is secured to the outer ring with a close running clearance to the inner ring.
Shielded bearings can be relubricated.
1. Retains the lubricant at the rolling elements regardless of the chamber fill.
2. Provides relubrication to the balls by the slinger feeding of inner ring.
3. Eliminates large particles from getting into the rolling elements at installation and in
4. Higher Friction Losses over open but typically less than Sealed Bearings.
Excessive pressure with no relief provided can force the shields against the cage or balls,
thereby, eliminating regreasability or causing immediate failure.
KML Bearing USA Inc.
Page 11
Angular Contact Ball Bearings (ACBB)
Angular contact ball bearings are designed to support axial loads in one direction or axial loads
combined with radial loads.
Contact angle: the angle between the line connecting the contact points of the ball and the inner
ring and the ball and the outer ring, and the line drawn in the radial direction. Angular contact
ball bearings have contact angles of 15º, 25º and 40º identified by suffix C, A and B respectively.
Angular contact ball bearings with the larger contact angles tolerate heavier axial loads.
Angular contact ball bearings have increased thrust capacity over Conrad bearings.
Thrust must be in the direction of the thrust shoulder. Thrust in an opposite direction can drive
balls over the counter-bore shoulder or cause ball damage, and failure.
These bearings can be mounted singularly or, when the side surfaces are flush ground, in
multiple, either face-to-face or back-to-back for all combinations of thrust and radial loading.
Flush ground bearings can also be tandem mounted to permit sharing heavy thrust loads in one
direction among two or more bearings.
KML Bearing USA Inc.
Page 12
Duplex angular contact ball bearings
a) Tandem Mounting (DT)
Can accommodate radial and single direction axial loads.
Can accommodate heavy axial loads as axial loads are received by both bearings
b) Back-to-back Mounting (DB)
o Can accommodate radial loads and axial loads in either direction.
o Has a large distance between the acting load center of the bearing, and therefore a
large moment capacity.
o Allowable misalignment angle is small.
c) Face-to-face Mounting (DF)
Can accommodate radial loads and axial loads in either direction.
Has a smaller distance between the acting load center of the bearing, and therefore a
smaller moment capacity.
Has a larger allowable misalignment angle than back-to-back type.
KML Bearing USA Inc.
Page 13
Double row angular contact ball bearings
The structure of double row angular contact ball bearings is designed by arranging two single
row angular contact ball bearings back-to-back (DB) to form one united bearing with a contact
angle of 25º.
They have the same characteristics as duplex angular contact ball bearings (DB), while having
smaller width. They are suited where axial space is limited.
For high speeds or high accuracy requirements, double row angular contact ball bearings are not
as good as single row or duplex angular contact ball bearings
KML Shielded and sealed type double row angular contact ball bearings are also available.
KML Notes
KML Bearing USA Inc.
Page 14
Thrust Ball Bearings
Thrust ball bearings ordinarily have a 90º contact angle.
Thrust ball bearings are divided into single direction and double direction type. The former only
supports axial loads in one direction, while the latter supports axial loads in both directions.
Thrust ball bearings permit only axial loads, and they are not recommended for high-speed
Single direction thrust ball bearings (51000 series)
Double direction thrust ball bearings (52000 series)
KML Bearing USA Inc.
Page 15
Self-Aligning Ball Bearings
Self-aligning ball bearings, with two rows of balls rolling on the spherical surface of the outer
ring, compensate for angular misalignment resulting from errors in mounting, shaft deflection, or
distortion of the foundation. It is impossible for these bearings to exert any bending influence on
the shaft.
The permissible misalignment of self-aligning ball bearings is approximately 3º under normal
It is a very important consideration in many applications requiring extreme accuracy, at high
speeds. Self-aligning ball bearings are recommended for radial loads and moderate thrust loads.
KML self-aligning ball bearings with tapered bores (1:12) are also available.
KML Bearing USA Inc.
Page 16
Roller Bearings
Cylindrical Roller Bearings
Cylindrical roller bearings can accommodate more radial loads (approximately 2 to 3 times) than
ball bearings. Ordinarily they are unable to accommodate even the slightest axial loads. Some
types which have ribs on the outer ring and the inner ring can receive axial loads.
The rollers are guided by ribs on either the inner or outer ring, therefore cylindrical roller
bearings are more suitable for high-speed applications.
Cylindrical roller bearings are separable and relatively easy to install and disassemble even
when interference fits are required.
Cylindrical roller bearings types:
KML Bearing USA Inc.
Page 17
Double row cylindrical roller bearings are also in use.
NN 0000 K
NNU 0000 K
NNU 0000
The permissible misalignment varies depending on the type and internal specifications. Under
normal loads, the misalignment angles are approximately as follows:
For width series 0 or 1: 2´
For width series 2: 4´
KML Notes
KML Bearing USA Inc.
Page 18
Tapered Roller Bearings
A large variety of tapered roller bearings, including single, double and four row arrangements are
in use both in metric and inch system sizes.
Tapered roller bearings can be disassembled into parts:
Inner ring, rollers, cage (collectively called as the “cone”)
Outer ring (called as the “cup”)
Subunit dimensions are standardized, therefore, they are interchangeable within each
dimensional standard. However, high precision grade bearings are generally not interchangeable.
Tapered roller bearings have a high capacity for radial loads, axial loads, and combined loads.
The larger the contact angle, the greater the axial load capacity becomes.
The cone and the cup are separable, enabling them to be installed with the desired interference
Double row (35000 series)
KML Bearing USA Inc.
Four row (38000 series)
Page 19
Spherical Roller Bearings
Spherical roller bearings have self-aligning properties. They are suitable for applications where
misalignment between the inner and out rings occurs from housing installation error or shaft
Spherical roller bearings have a large capacity for radial loads, axial loads in either direction, and
complex loads. They are also suited for use where vibration and shock loads are encountered.
It is possible to provide an oil groove and holes in the out ring to supply lubricant (with code
The permissible misalignment varies depending on the size and loads, but it is approximately 1º
to 2.5º with average loads.
In addition to spherical roller bearings with cylindrical bore diameters, those with tapered bore
diameters are also available at KML.
The suffix “K”: taper ratio 1:12 for bearings with tapered bores;
The suffix “K30”: taper ratio 1:30 for bearings with tapered bores;
KML Bearing USA Inc.
Page 20
Needle roller bearings
Needle roller bearings are bearings with rollers that have high length-to-diameter ratios.
Compared with other roller bearings, needle roller bearings have much smaller rollers for a given
bore size. Needle roller bearings have the highest load capacity for a given radial space of all
rolling element bearings.
All needle roller bearings are variations of two basic designs.
Loose - needle bearings are simply a full complement of needles in the annular space
between two hardened components and contain no retainer. Needle rolling bearings provide
an effective and inexpensive bearing assembly with moderate speed capability, but they are
sensitive to misalignment.
Caged needle bearings are simply a roller complement with a retainer or cage for roller
guidance and spacing. Their speed capability is about three times higher than that of loose needle bearings, but the smaller complement of needles reduces load capacity.
Needle roller bearings have the advantage of a higher speed capacity; also they have greater
lubricant capacity.
Needle roller bearings are mainly classified into four types shown below.
Needle roller and cage assemblies (K type)
Needle roller bearings with inner ring (type NA, NK1)
Needle roller bearings without inner ring (type RNA, NK)
Drawn cup needle roller bearings without inner ring (type HK, BK)
KML Bearing USA Inc.
Page 21
Roller Thrust Bearings
Roller thrust bearings include spherical roller thrust bearings, cylindrical roller thrust bearings,
tapered roller thrust bearings and needle roller thrust bearings.
Spherical roller thrust bearings combine a very high load-carrying capacity (heavy axial loads or
combined loads which are predominantly axial) with a self-aligning capability and can operate at
relatively high speeds under heavy loads.
Cylindrical roller thrust bearing, tapered roller thrust bearings and needle roller thrust bearings
can sustain only axial loads.
KML Bearing USA Inc.
Page 22
Rolling element linear bearings
Most rolling element bearings are in use for rotating or oscillating loads, but there are also
bearings designed for linear motion. Rolling element (ball or cross roller) linear bearings are
widely employed in the precision tables today.
Rolling element linear bearings are grouped into two primary categories: recirculating rolling
element linear bearings, and nonrecirculating rolling element linear bearings.
Recirculating rolling element linear bearings, which are sometimes called recirculating ball
bushings, facilitate very long travel distances. These ball bushings have several rows of
recirculating balls (balls circulate in a loop, each set in their own track), which support the
moving carriage and permit very long travel lengths. The ball bushings provide good load
capacity with very low friction (the coefficient of friction can be as low as 0.001) and its modular
design permits easy replacement of bearing components.
To minimize installation time and cost, the ball bushings can be mounted in industry standard
pillow blocks. The closed type and open type pillow blocks are available. The closed type is used
in end-supported applications for spanning or bridging a gap. While the open style is used for
continuously supported applications when maximum rigidity and stiffness is required.
KML Bearing USA Inc.
Page 23
Linear guides
Another rolling element linear bearings are linear guides. Linear guides are roller guides which
utilize balls and are used for supporting load and guiding precise linear motion with low friction.
Linear guides are comprised of a rail and ball slide. The balls roll on the grooves on the rail and
the ball slide, and are collected by the end cap. The end cap is attached to the end of the ball slide.
Then the balls go through the opening made in the ball slide, and circulate back to the other end.
Characteristics of linear guides:
o High precision and quality;
o High reliability and durability;
o High load carrying capacity (shock-resistance);
They can be used in Machine tools because of their high accuracy, high load capacity, high
speed, smooth motion, and high durability. Also they can be used in Carriers, handling robots,
and injection Molding machines, etc. Below is an example used in high accuracy positioning
KML Bearing USA Inc.
Page 24
Plain Bearings
There are three types of lubrication in plain bearings.
Boundary lubrication - bearing and shaft surfaces rub together with only a thin film of
lubricant separating them. Grease-lubricated bearings generally operate with a boundary
o Mixed-film lubrication - bearings support part of the loads on a boundary film where the
shaft is closest to the bearing. The remainder of the loads is supported by hydrodynamic,
or full-film, lubrication.
o Full-film or hydrodynamic lubrication - the shaft is separated from the bearing by a
continuous film of self-pressurized lubricant with no metal-to-metal contact. This fluid
film is generally about 0.001 in. thick, but films as thin as 0.0005 in. are sufficient if shaft
surface finish is held within 10-µm. RMS and bearing inner surface is held to 30-µm.
RMS maximum.
In many situations, the bearing itself contains or acts as the lubricant. Because most applications
exhibit less than full-film lubrication at least occasionally, a bearing of proper material and
design must be selected to ensure satisfactory operation.
Bearings operating with full-film lubrication typically exhibit a coefficient of friction between
0.001 and 0.020, depending on mating surfaces, lubricant, clearances, and speed. For a mixedfilm bearing, the coefficient ranges between 0.02 and 0.08, and for boundary-lubricated bearings,
between 0.08 and 0.14.
The coefficient of friction in a bearing application is important because the higher the coefficient
of friction, the higher the heat generation. Excessive heat reduces life of the bearing. Excessive
heat may also cause expansion of the shaft, housing, or bearing, or any combination of these.
This expansion reduces the clearance between the shaft and bearing, further increasing operating
temperature, resulting eventually in premature bearing failure.
Many metallic, nonmetallic, and compound materials are available. Bronze has probably been
the most familiar plain bearing material because a variety of characteristics can be imparted to it
by adding other metals. In general, softer materials are used for lighter loads and higher speeds;
harder materials for higher loads and lower speeds.
Metallic - The softest metallic bearing materials are babbitts. Babbitts have been widely used as
bearing materials for years.
In terms of increasing hardness, the next material family is bronze alloys, such as Tin bronze,
Manganese bronze, Aluminum bronze, sintered bronze, etc. They serve from very high-speed,
light-load uses to very light-speed, high-load uses.
KML Bearing USA Inc.
Page 25
Zinc-aluminum alloys have emerged in recent years as a cost-effective alternative to bronze
alloys; however, successful application of zinc-aluminum alloys is restricted primarily to highload, low-speed applications.
Nonmetallic - Nonmetallic or self-lubricating bearings often require no liquid lubricant. Selflubricating bearings are most effective in applications where relative motion is not sufficient to
circulate oil or grease required for metallic bearings. Self-lubricating bearings are also used for
temperatures beyond the scope of conventional lubricants. These temperatures may range from
400 to 750°F or higher. Self-lubricating bearings are especially well suited for corrosive
The coefficient of friction of self-lubricating bearings running completely dry generally ranges
from 0.1 to 0.4. Thus, Friction limits the application of self-lubricating bearings.
The most common self-lubricating materials include polytetrafluor-oethylene (PTFE), graphite,
and molybdenum disulfide (MoS2).
Spherical plain bearings
Spherical plain bearings have the inner and outer rings making contact with each spherical
surface and can take a large radial load and two directional thrust load at the same time.
Spherical plain bearings are basically divided into steel-on-steel and maintenance-free types
according to the kind of sliding surface.
1. The steel-on-steel type have inner and outer rings of high carbon chromium bearing steel
and the sliding surface has been phosphate-treated, and is dry-coated with molybdenum
disulfide (MoS2). They can, therefore, operate with low torque, and have excellent wear
resistance properties and a large load rating. They are especially suitable for applications
where there is alternate load and shock load.
2. The maintenance-free type is a combination of an outer ring which has a spherical
PTFE sheet fixed on the sliding surface, and a spherical inner ring whose sliding surface
has a hard chromium plating. They have a long life and can be used for extended periods
of time without re-lubrication. They are especially suitable in cases where fixed
directional loads are to be taken and are used mainly in foodprocessing machines and
construction machinery and other fields where the use of oil is undesirable and where
lubrication is not possible.
KML Bearing USA Inc.
Page 26
Technical Information
Bearing numbers
Rolling bearing numbers are comprised of “basic numbers” followed by “supplementary
symbols”. The basic numbers indicate the bearing type, the width series, diameter series (outer
diameter dimensions), bore diameter and contact angle. The supplementary codes derive from
prefixes and suffixes which identify detail characteristics of the bearings such as tolerances,
internal clearances, seal or shield specifications, etc.
Bearing type code
Deep groove ball bearings: 6
Angular contact ball bearings: 7
Self-aligning ball bearings: 1, 2
Cylindrical roller bearings: NU, N, NF, NNU, NN, etc.
Tapered roller bearings: 3
Spherical roller bearings: 2
Cylindrical roller thrust bearings: 8
Thrust ball bearings: 5
NR: with snap ring
ZZ: with double shields
2RS: with double non contact seals
2RD: with double light contact seals
2RK: with double contact seals
Contact angle code
Angular contact ball bearings:
A standard contact angle: 25º
B standard contact angle: 40º
C standard contact angle: 15º
o Tapered roller bearings:
(B) over 10 º to/including 17 º
C over 17 º to/including 24 º
D over 24 º to/including 32 º
KML Bearing USA Inc.
Page 27
Bearing number examples
6 3 0 6 ZZ C3
Radial internal clearance C3
Shields on both sides
Bearing bore diameter 30mm
Diameter series 3
Deep groove ball bearing
NN 3 0 0 6 K C1 P4
Accuracy of ISO Class 4
Radial internal clearance C1
Tapered inner ring bore (taper ratio 1:12)
Bearing bore diameter 30mm
Diameter series 0
Width series 3
Cylindric roller bearing NN type
7 2 0 6 A DB
Back-to-back duplex arrangement
Contact angle 25º
Bearing bore diameter 30mm
Diameter series 2
Angular contact ball bearing
KML Notes
KML Bearing USA Inc.
Page 28
Internal Clearance
Bearing internal clearance: the total amount that one ring can be displaced relative to the
other in the radial and axial directions before being installed on a shaft or in a housing
The radial internal clearance and the axial internal clearance
Internal clearance code: C2, (CN), C3, C4, C5
C2 - Radial clearance less than standard
No suffix - Radial clearance is standard
C3 - more than standard (Reliance Standard)
C4 - more than C3
Radial ball bearings are usually supplied with a specified radial clearance, which will normally
diminish during mounting because of interference fits with the shaft and house. After mounting,
the bearing should have a small radial clearance remaining.
1) Bearings are normally a press fit on the shaft of the rotating unit. The degree of press
stretches the inner ring O.D. - this can compress the balls and reduce life.
2) Heat caused by rotation can expand the balls and rings. To eliminate precompression of
balls, radial clearance should be allowed.
KML Bearing USA Inc.
Page 29
Bearing tolerances
Dimensional accuracy and running accuracy
o Dimensional accuracy is related to mounting of bearings on shafts or in housings
o Running accuracy is related to runout of rotating parts
ISO, DIN, and JIS standardize five classes of bearing tolerances: class 0,6,5,4,2, with
progressively higher degrees of precision
AFBMA standards:
ABEC 1, ABEC 3, ABEC 5, ABEC 7, ABEC 9 for Ball bearings
RBEC 1, RBEC 3, RBEC 5, for Roller bearings
AFBMA - Anti-friction Bearing Manufacturers Association
ABEC - Annular Bearing Engineering Committee
RBEC - Roller Bearing Engineering Committee
ISO - International Organization for Standardization
JIS - Japanese Industrial Standards
DIN - Deutsch Industrie Norm
tolerances suitable for general commercial applications such as
appliances, automobiles, and construction equipment
tolerances suitable for use in machine tools and high speed electric
for measuring and recording instruments and other precision equipment
4, 2
KML Bearing USA Inc.
Page 30
Boundary dimensions
The boundary dimensions of rolling bearings, sometimes referred to as the bearing’s envelope
dimensions, are the dimensions that define external geometry. They include Outside Diameter
D, Inside Diameter or bore d and width B and chamfer dimension r.
Bearing boundary dimensions have been standardized by the international Standards
Organization (ISO). Within each diameter series there are several dimension series which are
combinations of the diameter series and different width series.
KML Bearing USA Inc.
Page 31
Bearing Life
When a number of identical bearings are operated under the same conditions of load and speed, a
dispersion of their lives is observed.
Basic rating bearing life is based on a 90% statistical model which is expressed as the total
number of revolutions 90% of the bearings in an identical group, subjected to identical operating
conditions, will attain or exceed before flaking due to material fatigue occurs.
Other causes of bearing failure are attributed to problems such as seizing, abrasions, cracking,
chipping, rust, etc. Since these “causes” of bearing failure can be avoided by taking the proper
precautions, and are not simply caused by material fatigue, they are considered separately from
the flaking aspect.
Factors of lubrication, temperature, contaminants, etc., are not considered in this process.
Note that bearing life is a minimum design calculation and almost all bearings will have a life
exceeding this figure unless the bearing is subject to abnormal conditions.
The term B10 and L10 are used interchangeably. However, L10 is the current and correct
The relationship between the basic rating life, the basic dynamic rating and the equivalent load is
L10 = (Cr / Pr)
L10 :
Cr :
Pr :
p :
Basic rating life in 10 revolutions
Basic dynamic rating load
Equivalent load
=3 for ball bearings
=10/3 for roller bearings
KML Bearing USA Inc.
Page 32
Causes Of Bearing Failures
Almost without exception, the published life of a bearing is the L10 life based on the fatigue
failure of rings or rolling elements. Actually, it is very unusual to find a bearing that has failed
from this cause.
Bearing damage type
Small pieces of bearing material are split off from the smooth surface of the raceway or rolling
elements due to rolling fatigue.
Scoring is surface damage due to accumulated small seizures caused by sliding under improper
lubrication or under severe operating conditions. Linear damage appears circumferentialy on the
raceway and rolling surfaces. Cyclodial shaped damage on the roller end. Scoring on the rib
surface contacting roller end.
Smearing occurs from a collection of small seizures between bearing components caused by oil
film rupture and/or sliding. Surface roughening occurs along with melting.
Cracks can be in the raceway ring and rolling elements. Continued use under this condition
leads to larger cracks or fractures.
Raceways and rolling elements may become dented if the mounting pressure is applied to the
wrong ring, so that it passes through the rolling elements, or if the bearing is subjected to
abnormal loading while not running.
When sudden overheating occurs during rotation, the bearing becomes discolored. Next, the
raceway rings. The rolling elements and the cage will soften, melt and deform as damage
Electrical Corrosion
When electrical current passes through a bearing, arcing and burning occurs through the thin oil
film at points of contact between the race and rolling elements. The points of contact are melted
locally to form ‘fluting’ or groove-like corrugations.
KML Bearing USA Inc.
Page 33
Corrosion & Rust
Corrosion and rust are pits on the surface of rings and rolling elements and may occur at the
rolling element pitch on the rings or over the entire bearing surfaces.
Abnormal Wear (wear, creep, fretting)
Wear is surface deterioration due to sliding friction at the surface of the raceway, rolling
elements, roller end faces, rib face, cage pockets etc.
Creep is a relative slipping at the fitting surfaces. It occurs in operation when the fit is not tight
enough compared to the applied load.
Fretting corrosion occurs when a bearing in a stationary condition is subjected to vibration or
oscillation at a small angle.
The most common causes of failure are as follows:
Poor lubrication practices coupled with errors in specifying bearings cause 36% of premature
bearing failures. While sealed-for-life bearings can be fitted and forgotten, any bearing deprived
of proper lubrication will fail long before its normal service life.
Wherever manual maintenance is not feasible, a fully automatic lubrication system can be
installed to lubricate a bearing with the right amount of lubricant at the correct lubrication
intervals. Failure can be the result of using the wrong lubricant type, mixing lubricants, improper
re-lubrication amounts, and improper additives.
Premature Fatigue accounts for 34% of early bearing failures. Whenever machines are
overloaded, unbalanced, or misaligned, bearings suffer the consequences. These abnormal
conditions cause unintended loads on the bearing that can quickly add up to a dramatic reduction
in service life.
Due to overload bearings: An overloaded bearing can cause premature spalling, breakdown
of lubrication, excessive heat and failure of the bearing. Such an overload can be caused by
too tight a fit either on the shaft or in the housing, or by axial thermal expansion of the shaft.
Due to misalignment of components: One of the great causes of premature bearing failure is
misalignment between the equipment shaft and bearing housing bore. Some, but not all,
bearings can tolerate minor misalignment. Serious misalignments introduce excessive
vibration and loads.
Poor installation accounts for about 16% of all premature bearing failures. Service personnel
need to be aware of which tools to use and be trained in using them. Improper installation
techniques can lead to failures from load imbalance, misalignment, or improper load
distributions within the bearing.
KML Bearing USA Inc.
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Contamination contributes to about 14% of premature bearing failures. Bearing users have
sealing solutions available that can be tailored to the most arduous operating environments.
Typical failures can be the result of excessive wear, abnormal surface stresses caused by debris
denting, or corrosion from liquid contamination, such as water.
Other Causes of Bearing Failure
There are literally hundreds of reasons bearings go bad. Although most of these problems can be
spotted quickly, others are quite bewildering. At KML, we suggest detecting signs of bearing
failures by monitoring noise, vibration, temperature and lubrication. Thus, the possibility of
similar future failures can be reduced if all the conditions at the time of failure and the operating
environment are known.
KML Notes
KML Bearing USA Inc.
Page 35
Bearing Materials
Generally, the bearing materials are required to have the following properities.
1. High fatigue strength to bear repetition of high contact loads.
2. Corrosion-resistance or heat-resistance for some application.
3. High elastic limit to withstand high localized contact stress.
4. Hardenability to ensure sufficient hardness.
5. Toughness to accept impact loads.
6. Dimensional stability.
Rings and rolling element materials
1) High-Carbon Chrome Bearing Steel
A large majority of rolling bearings use high-carbon chrome steel. KML specifies the chemical
composition of this materical as follows.
Chemical Composition of High-Carbon Chrome Steel
0.98/1.10 0.25/0.45 0.15/0.35 1.30/1.60 <=0.025
<=0.25 <=0.35 <=0.10
0.95/1.05 0.25/0.45 0.15/0.35 1.40/1.65 <=0.025
<=0.30 <=0.25 <=0.08
0.95/1.05 0.95/1.25 0.45/0.75 1.40/1.65 <=0.025
<=0.30 <=0.25 <=0.08
GCr15SiMn contains large amount of manganese to improve hardenability, and is used to
manufacture heavy section bearing rings. When the wall thickness of the rings required is under
17mm, GCr15 is applied, when it exceeds 17mm, GCr15SiMn is used.
2) Carburized Steel (Case Hardened Steel)
Because of its combination of a hard surface layer which has been carburized and a relatively
pliable inner core, Carburized Steel has excellent efficiency against shock loads. Typical
Carburized Steel are chrome steel and chrome molybdenum steel.
3) Heat Resistant Bearing Steel
When bearings made of ordinary chrome steel which have undergone standard heat treatment are
used at temperatures above 120°C for long durations, unacceptably large dimensional changes
can occur. For this reason, a dimension stabilizing treatment has been devised for high
temperature applications. A variety of heat resistant steels are incorporated in bearings to
minimize softings and dimensional changes when used at high temperatures, i.e. high speed
molybdenum steel and high speed tungsten steel
4) Corrosion Resistant Bearing Steel
For applications requiring high corrosion resistance, stainless steel is used. To achieve this
corrosion resistance a large porportion of alloying element chrome is added to martensite
stainless steel.
KML Bearing USA Inc.
Page 36
Retainer Materials
As the retainer may have a substantial influence on the bearing performance and reliability,
selection of its material is also important.
Retainers are subdivided into pressed cages and solid cages. When compared with machined
cages of metal, pressed cages are advantageous in that they are lighter in weight.
Machined cages of metal are used when requirements in cage strength are strict and temperatures
are high.
For small and medium sized bearings, pressed cages with a low content of approximately 0.1%
carbon are used, i.e. steel 08, 10, etc.
For large bearings, machined cages of structural carbon steel or high tensile case brass are widely
used, i.e. steel 40, 45, etc.
Plastic materials may be chosen depending on application conditions, such as polyamide 66.
KML Notes
KML Bearing USA Inc.
Page 37
Bearing Units
At KML, The following types are available.
Pillow blocks
Flange units
Take-up units
Cartridge units
Hanger units
Methods of mounting to the shaft
Set screw locking
For set screw locking types, the inner ring of the bearing unit are hardened in the raceway
and surrounding part where hardening is necessary, while the extended part where the set
screws are installed is left metallurgically mild and tenacious.
The construction of the KML “Knurled cup point set screw” is illustrated below with a pin
design that prevents it from becoming loose even when it is subjected to vibrations or impact
To mount the set screw locking bearing unit on the shaft, it is sufficient to tighten the two set
screws uniformly using a hexagonal bar wrench.
Eccentric locking Collar
The inner ring is fastened on the shaft by fastening the eccentric collar in the direction of the
rotation of the shaft. Deformation of the inner ring seldom occurs.
Eccentric locking Collar bearing unit is not recommended for applications where the
direction of rotation is sometimes reversed.
Tighten the eccentric collar by inserting a bar into the hole provided on the periphery of the
eccentric collar and tapping the bar to turn the collar, and fasten the set screw of the eccentric
When an adapter bearing unit is used, there is no danger of the fit between the shaft and the
inner ring working loose even if it is subjected to impact loads or vibration.
After tighting the nuts, bend up the rim of the washer within the notch of the nut. This will
prevent the nut from loosening.
It is necessary to ensure that the nut is not over-tightened as this will deform the inner ring,
causing heat generation and seizure.
KML Bearing USA Inc.
Page 38
Grease fitting for relubrication
Combination of steel slinger
and steel-backed synthetic
rubber seal provides the most
effective sealing
Single row deep groove
ball bearing
Fully self-aligning
Rigid one-piece cast
Specially heat-treated wide
inner ring
KML Bearing USA Inc.
Knurled cup point set
screw 120° apart
Page 39
Pillow Blocks
Housing type
TB: Tapped base inch bolt holes
PE: Standard pillow blocks
AK: Lower base pillow blocks
PA: Tapped base metric bolt holes
PP: Pressed steel Pillow Blocks
Below are some examples of pillow blocks.
At KML, we supply a large variety of Pillow Blocks such as UCPE, SBPE, HCPE, SAPE,
KML Bearing USA Inc.
Page 40
Flange units
Housing type
F: Four Bolt Flange (square)
FS: Four Bolt Flange (square); FS is higher than F type
FC: Flange Cartridge (round)
FCS: Flange Cartridge (round); FCS is smaller than FC type
FL: Two Bolt Flange (rhombic)
FT: Two Bolt Flange (rhombic); FT is higher than FL type
FD: Two Bolt Flange (rhombic); more compact, no obvious flange
LF: Two Bolt Flange (rhombic); more compact
RFT: Triangle Flange
FB: Three bolt Flange Bracket (offset)
FK: Three bolt Flange Bracket (offset); the flange is higher than FB
FA: Adjustable Flange (skewing)
PF: Pressed Round Flange (round)
PFL: Pressed Two Bolt Flange
PFT: Pressed Triangle Flange
KML Bearing USA Inc.
Page 41
Take-up units
Housing type
ST: Take-up with Wide Slot
T: Take-up with Narrow Slot
Cartridge units
• Housing:
C: Cylindrical Cartridge
KML Bearing USA Inc.
Page 42
Hanger units
• Housing:
HA: Hanger
Ball Bearings for Units
Bearing type:
UC: Set Screw
SB: Set Screw flash on one side
CSB: Cylindrical Set Screw flash on one side
HC: Eccentric Collar
SA: Eccentric Collar flash on one side
CSA: Cylindrical Eccentric Collar flash on one side
KML Bearing USA Inc.
Page 43
Bearing Units
Housing Type of Mounted Bearing Units
Normal Height
with Reinforced
Low Base
Tap Base
4-Bolt Square
4-Bolt Round
Flange with
Spigot Joint
3-Bolt Triangle
Offset Flange
Pressed Steel
Hanger Type
Cyclindrical Cartridge
Take-up Type
Rubber Cartridge
Insert Bearings for Mounted Units
Insert Bearings
KML Bearing USA Inc.
Page 44
Corrosion Resistant Mounted Bearing Units
Specifications: KML 440C Grade Stainless Steel Bearings are filled with FoodRex FG1
food grade grease which is approved by the FDA and HACCP. The housings are made
from Thermo Plastic or Stainless Steel depending on the specifications of the application.
Applications: These mounted bearing units are suitable for use in various applications
where they are exposed to moisture, corrosive elements and/or abrasive conditions.
Typical Corrosion Resistant Applications
● Food processing plants
● Food packing plants
● Beverage, brewing and bottling plants
● Meat, poultry, and seafood processing plants
● Dairy industry plants
● Sugar processing plants
● Pharmaceutical plants
● Chemical plants
Corrosion Resistant
● Rubber and plastics plants
● Pulp and paper mills
● Marine and naval applications
● Car wash equipment
● Refrigeration and thermal equipment
● Agricultural harvesting equipment
● Municipal maintenance equipment
● Material handling machinery and conveyors
Base Pillow
Stainless Steel Housing
Thermo Plastic Housing
KML Bearing USA Inc.
Page 45
Introduction of KML Bearing:
KML specializes in manufacturing and providing logistics solutions for premium
quality bearings in a wide variety of styles and types. KML Bearing has a history of
accomplishments in the global bearing industry.
1980: The Company was established in Hong Kong.
1984: KML founded the first joint venture factory in Shekou, China for the production of
taper roller bearings. Production lines were imported from NTN, Japan.
1985: The second KML joint venture was founded in Yangchun, China. Ball bearing
production lines were imported from Italy and Japan.
1987: Established the Research & Development Department, now known as KML Technical
Center, for new product ventures.
1989: We designed and manufactured the fully automated cleaning, greasing and assembly
production line for ball bearings, which was a breakthrough technology in China at that time.
1992: KML was formally adopted as the brand name of our products. Another joint venture
factory was founded in Chongquing, China. This facility is noted for the high level of
automation in the production process with OEM product capabilities.
1993: KML Bearing Canada was founded in Montreal, Canada.
1996: KML Bearing Canada was relocated to Mississauga (Toronto), Canada.
1997: Established KML Logistics Offices in Guangzhou and Shanghai, China.
1999: KML Bearing & Equipment and joint venture facilities are ISO 9002 accredited.
2000: KML adopted the e-business strategy which committed the company to embrace
internet enabled business and communication processes.
2001: Wheel bearing hub assembly of original equipment designs are introduced to the
product lines.
2003: The full program of high-speed, high-temperature ball bearings for automotive / truck
underhood applications are developed.
2005: Resources are committed to establish U.S. subsidiary – KML Bearing USA with the
goal of establishing the KML brand in the Power Transmission Distribution and select OEM
2006: Ground is broken at a greenfield site for KML Powertech Ltd. joint venture factory in
Luoyang High Technology Region, Henan, China.
KML Bearing USA Inc.
Page 46
KML Mission
Our mission is the continuous development of our company into a
worldwide supplier of power transmission products built on customer
focused services through the incorporation of western business
KML Philosophy
Meet or exceed the customers’ expectations through convenient &
efficient services and continuous improvement.
Reduce total cost of acquisition through comprehensive product
lines and manufacturing excellence.
Provide an integrated logistics network that provides global scope
with local warehousing, packaging and inventory management.
Provide reliable, timely, customer-focused services and project
Integrate western business practices with Chinese resources.
Establish relationships with key business partners.
KML Bearing Group
KML Bearing & Equipment Ltd. - Hong Kong, China
KML Powertrans Inc. - Guangzhou, China
KML Powertech Ltd. - Louyang, China
KML Bearing Canada - Mississauga (Toronto), Canada
KML Bearing USA - Pottstown, PA
KML Bearing USA
213 Jones Boulevard
Pottstown, PA 19464
Phone: (610) 495-6134
Fax: (610) 495-6183
Copyright© 2006
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