Ball and Roller Bearings
- Angular Contact Bearings
- Ball Bearings
- Cam Follower
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- Double Row Bearings
- Instrument/ Miniature Bearings
- Needle Roller Bearings
- Rod End
- Roll Neck Bearings
- Self-Aligning, Self-Lubricating Bearings
- Shaker Screen
- Spherical Roller Bearings
- Steel Mill Bearings
- Super Precision / Precision / Metric Bearings
- Tape Thrust Bearings
- Taper Roller Bearings
- Thin Section Ball Bearings
- Z-Mill Bearings
Mounted Bearing Units
- Cartridge
- Flange Block Bearings
- Pillow Block Bearings
- Split Bearings
- Take-up Bearings
Lubricated Bearings
- Babbitt Bearings
- Bronze Bearings
- High-Temperature Bearings
- Journal Bearings
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Specialty Bearings
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Armoloy
AST Bearings
ATS Electro-lube
Auburn Ball Bearing
Aurora Bearing Company
Ball & Roller Bearing
Barden Precision Bearings
Bayside Motion Group
Beemer Precision
Berliss Bearing Company
Bishop-Wisecarver Corporation
Boston Gear
Bower
Browning Manufacturing
Bunting Bearing Corporation
Cignys
Cone Mounter Company
Cooper Bearing Company
Craft Bearing Company, Inc.
Danaher Motion (Thomson)
Dodge
EBC
Emerson Power Transmission
Corp.
Fafnir Bearings
FAG Bearings Corporation
Federal-Mogul Corporation
FKI Logistex
Frantz Manufacturing
Frost, Inc.
FYH Bearings
Garlock Bearings, Inc.
General Bearing Company
GMN
Hub City
Igus
IKO International, Inc.
INA Bearing Company, Inc.
IPTCI Bearings
Isostatic Industries, Inc.
JLV Engineering
Kaydon Corporation
Ketchie Houston
Kilian
AST Bearings
ATS Electro-lube
Auburn Ball Bearing
Aurora Bearing Company
Ball & Roller Bearing
Barden Precision Bearings
Bayside Motion Group
Beemer Precision
Berliss Bearing Company
Bishop-Wisecarver Corporation
Boston Gear
Bower
Browning Manufacturing
Bunting Bearing Corporation
Cignys
Cone Mounter Company
Cooper Bearing Company
Craft Bearing Company, Inc.
Danaher Motion (Thomson)
Dodge
EBC
Emerson Power Transmission
Corp.
Fafnir Bearings
FAG Bearings Corporation
Federal-Mogul Corporation
FKI Logistex
Frantz Manufacturing
Frost, Inc.
FYH Bearings
Garlock Bearings, Inc.
General Bearing Company
GMN
Hub City
Igus
IKO International, Inc.
INA Bearing Company, Inc.
IPTCI Bearings
Isostatic Industries, Inc.
JLV Engineering
Kaydon Corporation
Ketchie Houston
Kilian
Koyo Corporation of USA
Link Belt
LM76 Linear Motion Bearings
MB Manufacturing, Inc.
McGill Bearings
Miether Bearing Products, Inc.
Miniature Precision Bearings
Moline Bearing Company
Morse Industrial
MRC Bearings
Nachi America Inc.
Nice
Nilos
Nolu Plastics
NSK Corporation
NTN Bearing Corporation of
America
Osborn International
Pacific Bearing Company
Pacific Bearing Simplicity
PCI (Pro Cal Inc.)
Phymet, Inc.
PT International
QM Bearings
Randall Bearings, Inc.
RBC Bearings
Rexnord Corporation
RHP Bearings
Rollway Bearing Company
Scheerer Bearing
Schrade Ball Bearing
SealMaster
SKF, Inc.
Spadone Alfa
Split Ball Bearing
SST Bearing Corporation
Standard Locknut, Inc.
The Timken Company
The Torrington Company
THK America, Inc
Thomson Industries Inc.
Torque Transmission
UTA-Cobra
Link Belt
LM76 Linear Motion Bearings
MB Manufacturing, Inc.
McGill Bearings
Miether Bearing Products, Inc.
Miniature Precision Bearings
Moline Bearing Company
Morse Industrial
MRC Bearings
Nachi America Inc.
Nice
Nilos
Nolu Plastics
NSK Corporation
NTN Bearing Corporation of
America
Osborn International
Pacific Bearing Company
Pacific Bearing Simplicity
PCI (Pro Cal Inc.)
Phymet, Inc.
PT International
QM Bearings
Randall Bearings, Inc.
RBC Bearings
Rexnord Corporation
RHP Bearings
Rollway Bearing Company
Scheerer Bearing
Schrade Ball Bearing
SealMaster
SKF, Inc.
Spadone Alfa
Split Ball Bearing
SST Bearing Corporation
Standard Locknut, Inc.
The Timken Company
The Torrington Company
THK America, Inc
Thomson Industries Inc.
Torque Transmission
UTA-Cobra
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Knowledge Base
A ball bearing is an engineering term referring to a type of rolling-element bearing which uses balls to maintain the separation
between the moving parts of the bearing.
The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least
two races to contain the balls and transmit the loads through the balls. Usually one of the races is held fixed. As one of the
bearing races rotates it causes the balls to rotate as well. Because the balls are rolling they have a much lower coefficient of
friction than if two flat surfaces were rotating on each other.
Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller
contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races.
Compared to other bearing types, the ball bearing is the least expensive, primarily because of the low cost of producing the
balls used in the bearing.
History
Leonardo da Vinci has been credited with the discovery of the principle behind the mechanics of ball bearings[citation needed].
The first patent was awarded to Jules Suriray, a Parisian bicycle mechanic, on 3rd August 1869. The bearings were then fitted
to the winning bicycle ridden by James Moore in the world's first bicycle road race, Paris-Rouen, in November 1869.
The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907.
Ball bearings were found on the Roman Nemi ships constructed in about 40 A.D.
Common designs
There are several common designs of ball bearings, each offering various tradeoffs. They can be made from many different
materials, including: stainless steel, chrome steel, and ceramic (silicon nitride (Si3N4)). A hybrid ball bearing is a bearing with
ceramic balls and races of metal.
Angular contact
An angular contact ball bearing uses axially asymmetric races. An axial load passes in a straight line through the bearing,
whereas a radial load takes an oblique path that tends to want to separate the races axially. So the angle of contact on the
inner race is the same as that on the outer race. Angular contact bearings better support "combined loads" (loading in both the
radial and axial directions) and the contact angle of the bearing should be matched to the relative proportions of each. The
larger the contact angle (typically in the range 10 to 45 degrees), the higher the axial load supported, but the lower the radial
load. In high speed applications, such as turbines, jet engines, dentistry equipment, the centrifugal forces generated by the
balls will change the contact angle at the inner and outer race. Ceramics such as silicon nitride are now regularly used in such
applications due to its low density (40% of steel - and so significantly reduced centrifugal force), its ability to function in high
temperature environments, and the fact that it tends to wear in a similar way to bearing steel (rather than cracking or shattering
like glass or porcelain).
Most bicycles use angular-contact bearings in the headsets because the forces on these bearings are in both the radial and
axial direction.
Axial
An axial ball bearing uses side-by-side races. An axial load is transmitted directly through the bearing, while a radial load is
poorly-supported, tends to separate the races, and anything other than a small radial load is likely to damage the bearing.
Deep-groove
A deep-groove radial bearing is one in which the race dimensions are close to the dimensions of the balls that run in it.
Deep-groove bearings have higher load ratings for their size than shallow-groove , but are also less tolerant of misalignment of
the inner and outer races. A misaligned shallow-groove bearing may support a larger load than a similar deep-groove bearing
with similar misalignment.
Conrad
A Conrad bearing is assembled by placing the inner and outer races radially offset, so the races touch at one point and have a
large gap on the radially opposite side. The bearing is then filled by placing balls in to the large gap, then distributing them
around the bearing assembly. The act of distributing the balls causes the inner and outer races to become concentric. If the
balls were left free, the balls could resume their offset locations and the bearing could disassemble itself. Thus, a cage is
inserted to hold the balls in their distributed positions. The cage supports no bearing load; it serves to keep the balls located.
Conrad bearings have the advantage that they take both radial and axial loads, but the disadvantage they cannot be filled to a
full complement and thus have reduced load-carrying capacity compared to a full-complement bearing. The Conrad bearing is
named for its inventor, Robert Conrad, who got British patent 12,206 in 1903 and U.S. patent 822,723 in 1906. Probably the
most familiar industrial ball bearing is the deep-groove Conrad style. The bearing is used in most of the mechanical industries.
Slot-fill
A slot-fill radial bearing is one in which the inner and outer races are notched so that when they are aligned, balls can be
slipped in the slot in order to fill the bearing. A slot-fill bearing has the advantage that the entire groove is filled with balls, called
a full complement. A slot-fill bearing has the disadvantages that it handles axial loads poorly, and the notches weaken the
races. Note that an angular contact bearing can be disassembled axially and so can easily be filled with a full complement.
Split-race
The outer race may be split axially or radially, or a hole drilled in it for filling. These approaches allow a full complement to be
used, but also limit the orientation of loads or the amount of misalignment the bearing can tolerate. Thus, these designs find
much less use.
Single-row versus double-row
Most ball bearings are single-row designs. Some double-row designs are available but they need better alignment than
single-row bearings.
Caged
Caged bearings typically have fewer balls than a full complement, and thus have reduced load capacity. However, cages keep
balls from scuffing directly against each other and so can reduce the drag of a loaded bearing. Caged roller bearings were
invented by John Harrison in the mid 1700s as part of his work on chronographs.[4] Caged bearings were used more frequently
during wartime steel shortages for bicycle wheel bearings married to replaceable cups.
Ceramic hybrid ball bearings using ceramic balls
Ceramic bearing balls weigh up to 40% less than steel bearing balls, depending on size. This reduces centrifugal loading and
skidding, so hybrid ceramic bearings can operate 20% to 40% faster than conventional bearings. This means that the outer
race groove exerts less force inward against the ball as the bearing spins. This reduction in force reduces the friction and
rolling resistance. The lighter ball allows the bearing to spin faster, and uses less energy to maintain its speed.
Ceramic hybrid ball bearings use these ceramic balls in place of steel balls. They are constructed with steel inner and outer
rings, but ceramic balls; hence the hybrid designation.
Modern Applications
Today the ball bearing is used in numerous applications which affect the functionality of everyday life. One interesting
application for ball bearings has been implemented at the San Francisco International Airport. In the airport there are 267
columns which are used to bear the weight of the airport. Each column is placed on a steel ball bearing with a diameter of 5
feet. The ball sits in a concave foundation. If an Earthquake occurs, the ground can move up to 20 inches in any direction, as
the columns roll on their bases. This is an effective way to separate the building from the movement of the ground. After the
earthquake has ended, the columns are re-centered on their bases by the force of gravity.
Ball bearings are also used for dental and medical instruments. In dental and medical hand pieces, it is necessary for the
pieces to withstand sterilization and corrosion. Because of this requirement, dental and medical hand pieces are made from
440C stainless steel, which allows for smooth rotations at fast speeds.
Hard drive bearings used to be highly spherical, and were said to be the best spherical manufactured shapes, but this is no
longer true, and more and more are being replaced with fluid bearings.
German ball bearing factories were often a target of allied aerial bombings during World War II; such was the importance of the
ball bearing to the German war industry.
A ball bearing is an engineering term referring to a type of rolling-element bearing which uses balls to maintain the separation
between the moving parts of the bearing.
The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least
two races to contain the balls and transmit the loads through the balls. Usually one of the races is held fixed. As one of the
bearing races rotates it causes the balls to rotate as well. Because the balls are rolling they have a much lower coefficient of
friction than if two flat surfaces were rotating on each other.
Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller
contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races.
Compared to other bearing types, the ball bearing is the least expensive, primarily because of the low cost of producing the
balls used in the bearing.
History
Leonardo da Vinci has been credited with the discovery of the principle behind the mechanics of ball bearings[citation needed].
The first patent was awarded to Jules Suriray, a Parisian bicycle mechanic, on 3rd August 1869. The bearings were then fitted
to the winning bicycle ridden by James Moore in the world's first bicycle road race, Paris-Rouen, in November 1869.
The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907.
Ball bearings were found on the Roman Nemi ships constructed in about 40 A.D.
Common designs
There are several common designs of ball bearings, each offering various tradeoffs. They can be made from many different
materials, including: stainless steel, chrome steel, and ceramic (silicon nitride (Si3N4)). A hybrid ball bearing is a bearing with
ceramic balls and races of metal.
Angular contact
An angular contact ball bearing uses axially asymmetric races. An axial load passes in a straight line through the bearing,
whereas a radial load takes an oblique path that tends to want to separate the races axially. So the angle of contact on the
inner race is the same as that on the outer race. Angular contact bearings better support "combined loads" (loading in both the
radial and axial directions) and the contact angle of the bearing should be matched to the relative proportions of each. The
larger the contact angle (typically in the range 10 to 45 degrees), the higher the axial load supported, but the lower the radial
load. In high speed applications, such as turbines, jet engines, dentistry equipment, the centrifugal forces generated by the
balls will change the contact angle at the inner and outer race. Ceramics such as silicon nitride are now regularly used in such
applications due to its low density (40% of steel - and so significantly reduced centrifugal force), its ability to function in high
temperature environments, and the fact that it tends to wear in a similar way to bearing steel (rather than cracking or shattering
like glass or porcelain).
Most bicycles use angular-contact bearings in the headsets because the forces on these bearings are in both the radial and
axial direction.
Axial
An axial ball bearing uses side-by-side races. An axial load is transmitted directly through the bearing, while a radial load is
poorly-supported, tends to separate the races, and anything other than a small radial load is likely to damage the bearing.
Deep-groove
A deep-groove radial bearing is one in which the race dimensions are close to the dimensions of the balls that run in it.
Deep-groove bearings have higher load ratings for their size than shallow-groove , but are also less tolerant of misalignment of
the inner and outer races. A misaligned shallow-groove bearing may support a larger load than a similar deep-groove bearing
with similar misalignment.
Conrad
A Conrad bearing is assembled by placing the inner and outer races radially offset, so the races touch at one point and have a
large gap on the radially opposite side. The bearing is then filled by placing balls in to the large gap, then distributing them
around the bearing assembly. The act of distributing the balls causes the inner and outer races to become concentric. If the
balls were left free, the balls could resume their offset locations and the bearing could disassemble itself. Thus, a cage is
inserted to hold the balls in their distributed positions. The cage supports no bearing load; it serves to keep the balls located.
Conrad bearings have the advantage that they take both radial and axial loads, but the disadvantage they cannot be filled to a
full complement and thus have reduced load-carrying capacity compared to a full-complement bearing. The Conrad bearing is
named for its inventor, Robert Conrad, who got British patent 12,206 in 1903 and U.S. patent 822,723 in 1906. Probably the
most familiar industrial ball bearing is the deep-groove Conrad style. The bearing is used in most of the mechanical industries.
Slot-fill
A slot-fill radial bearing is one in which the inner and outer races are notched so that when they are aligned, balls can be
slipped in the slot in order to fill the bearing. A slot-fill bearing has the advantage that the entire groove is filled with balls, called
a full complement. A slot-fill bearing has the disadvantages that it handles axial loads poorly, and the notches weaken the
races. Note that an angular contact bearing can be disassembled axially and so can easily be filled with a full complement.
Split-race
The outer race may be split axially or radially, or a hole drilled in it for filling. These approaches allow a full complement to be
used, but also limit the orientation of loads or the amount of misalignment the bearing can tolerate. Thus, these designs find
much less use.
Single-row versus double-row
Most ball bearings are single-row designs. Some double-row designs are available but they need better alignment than
single-row bearings.
Caged
Caged bearings typically have fewer balls than a full complement, and thus have reduced load capacity. However, cages keep
balls from scuffing directly against each other and so can reduce the drag of a loaded bearing. Caged roller bearings were
invented by John Harrison in the mid 1700s as part of his work on chronographs.[4] Caged bearings were used more frequently
during wartime steel shortages for bicycle wheel bearings married to replaceable cups.
Ceramic hybrid ball bearings using ceramic balls
Ceramic bearing balls weigh up to 40% less than steel bearing balls, depending on size. This reduces centrifugal loading and
skidding, so hybrid ceramic bearings can operate 20% to 40% faster than conventional bearings. This means that the outer
race groove exerts less force inward against the ball as the bearing spins. This reduction in force reduces the friction and
rolling resistance. The lighter ball allows the bearing to spin faster, and uses less energy to maintain its speed.
Ceramic hybrid ball bearings use these ceramic balls in place of steel balls. They are constructed with steel inner and outer
rings, but ceramic balls; hence the hybrid designation.
Modern Applications
Today the ball bearing is used in numerous applications which affect the functionality of everyday life. One interesting
application for ball bearings has been implemented at the San Francisco International Airport. In the airport there are 267
columns which are used to bear the weight of the airport. Each column is placed on a steel ball bearing with a diameter of 5
feet. The ball sits in a concave foundation. If an Earthquake occurs, the ground can move up to 20 inches in any direction, as
the columns roll on their bases. This is an effective way to separate the building from the movement of the ground. After the
earthquake has ended, the columns are re-centered on their bases by the force of gravity.
Ball bearings are also used for dental and medical instruments. In dental and medical hand pieces, it is necessary for the
pieces to withstand sterilization and corrosion. Because of this requirement, dental and medical hand pieces are made from
440C stainless steel, which allows for smooth rotations at fast speeds.
Hard drive bearings used to be highly spherical, and were said to be the best spherical manufactured shapes, but this is no
longer true, and more and more are being replaced with fluid bearings.
German ball bearing factories were often a target of allied aerial bombings during World War II; such was the importance of the
ball bearing to the German war industry.
1.800.409.3632
For outside the USA call: 1-866-941-5958
Best Practices for Storage, Handling and Installation
Rolling-element bearings are highly precise components with internal tolerances on the order of millionths of an inch. So they
should be handled carefully to ensure that they perform as expected.
The critical factor in ensuring that a rolling element bearing reaches its expected life is cleanliness, before, during and after it
is installed. Cleanliness is important because once dirt or debris enters a bearing, it acts like an efficient lapping compound.
Even minute amounts of lint mixed with a lubricant can create an abrasive mixture.
Contaminants are generally miscellaneous particles that, when trapped inside a bearing, permanently indent rolling elements
and raceways under the tremendous pressure generated. Because of the relatively small contact area between rolling
elements and raceway, contact pressures are extremely high, even for lightly loaded bearings. When rolling elements roll over
contaminants, contact areas are greatly reduced, and pressure is extremely high.
When abrasive material contaminates the lubricant, it is crushed into fine particles that wear the rolling elements and
raceways. Therefore, it is important to maintain a clean environment when working on bearings. The assembly area should be
isolated from all sources of contamination, including moisture and corrosive elements. Workbenches, tools, clothing and hands
should be free of dirt, lint, dust and other contaminants that may harm the bearing. The work surface should be clean and
rubber coated if possible. Plastic coating is also a good idea. This helps avoid nicking spindle parts on hard surfaces and
allows the work surface to be wiped clean periodically. In addition, plastic and rubber coatings can be replaced easily and
economically.
Also, never remove a bearing from its carton before it is to be used because moisture and dirt can contaminate the bearing.
Bearings are wrapped in a special neutral, acid-free paper, and they should be rewrapped in such paper for storage. They
should never be stored unwrapped, and they should never be wrapped in plastic. Plastic traps moisture that can rust the
bearing.
Bearings shipped from the manufacturer are packed with a rust preventative to prevent corrosion. This rust preventative is
compatible with common oils and greases, and need not be removed prior to installation.
When personnel handle clean bearings, particularly the rolling surfaces of separable bearings, they should wear surgical
gloves. This prevents acid from the skin from leaving a deposit that can stain the bearing surface, leading to etching and
corrosion. If gloves are not available, hands should be clean and dry.
Cleanliness is important not only for bearings, but also for shafts and housings. Dirt on the shaft can be pushed to the
shoulder during bearing mounting, preventing proper seating and leading to possible fretting corrosion due to loose fits.
Proper Installation
Several studies have shown that poor handling, particularly during installation, accounts for a high percentage of bearing
failures. Depending on bearing type and size, mechanical, hydraulic or thermal methods are used for mounting. Regardless of
the mounting method, care must be taken to prevent bearing rings, cages and rolling elements from receiving direct blows,
and mounting force should not be directed through the rolling elements.
Mounting should preferably be done in a dry, dust-free room away from metalworking or other machines producing swarf and
dust. When a bearing must be mounted in an unprotected area, which is often the case for large bearings, steps should be
taken to protect the bearing and mounting position from contamination by dust, dirt and moisture until installation has been
completed. This can be done by covering or wrapping bearings and machine components with waxed paper or foil.
Foreign matter entering a bearing shortens life and causes one or all of the following operating conditions:
• Increased noise
• Increased friction
• Ball skidding
• Increased heat
• Reduced lubricant life
Bearings under four inches in diameter are usually cold press-fitted onto the rotating member. If the shaft rotates, press on the
inner ring; if the housing rotates, press on the outer ring. Pushing on the wrong ring forces the rolling elements to indent the
raceway, a condition called brinelling.
Bearings with large inner ring interference (and large bore bearings) require a considerable amount of force to mount at room
temperature. Heating to expand the inner ring eases assembly in these cases. The recommended method for heating up a
bearing for installation is an induction heater. A suitable induction heater will be equipped with a temperature sensor to attach
to the inner ring and a de-magnetization cycle.
Double-seal and double-shield bearings should not be heated above 250°F (120°C) to avoid damaging the seals or the
special grease they are packed with.
An induction heater is essentially a transformer that induces low-voltage, high-amperage energy into the bearing races,
resulting in quick, even heating. It is essential to apply heat uniformly throughout the entire bearing. Torches should never be
used to heat the inner ring during installation because they produce high localized heat that can damage bearing components
and the lubricant.
Pay special attention to the shaft condition when installing a bearing. Dirt or a burr on the shaft can create a stress riser that
can cause the bearing to fail quickly due to local overload.
Pillow block and flange bearings require some special attention to ensure that they are securely locked to the shaft. The most
widely used method of locking the inner ring to the shaft employs an inner ring with locking set screw. The preferred locking
mechanism for a mounted unit is a concentric locking sleeve.
Tapered bore ball bearings and spherical roller bearings can be mounted on a tapered shaft or with an adapter that has a
corresponding taper on the OD of the split sleeve.
During installation of tapered ball bearings, they should be tightened until there is a slight drag on the outer ring, then the
washer tang can be set. With spherical roller bearings, the unloaded side of each bearing should be measured and a
recommended amount of clearance removed before installation. Never mount a spherical roller bearing while the load is
applied to the bearing.
The inner ring of bearings with tapered bores is always mounted with an interference fit. The degree of interference is
determined by how far the bearing is driven onto the tapered seat on the shaft or onto the adapter or withdrawal sleeve. This
process reduces radial internal clearances. The amount of reduction provides information on the fit produced. Bearing
manufacturers publish guidelines on how much these clearances can be reduced without affecting performance.
Small bearings can be driven onto a tapered journal or withdrawal sleeve using a nut; they can be driven onto adapter sleeves
using the sleeve nut. A hook spanner or impact spanner can be used to tighten the nut. The seating surfaces of the shaft and
sleeve should be lightly oiled before mounting.
Larger bearings require considerably more force for mounting. Hydraulic nuts and oil injection equipment ease this process.
Misalignment and Loose Fits
Correct alignment is critical for bearings to operate properly. The misalignment capability of the bearing is determined by the
type and series of the bearing. Misalignment can cause an abnormal temperature rise in the bearing or housing and heavy
wear in the cage pockets of rolling elements. Misalignment can be detected on the raceway of the non-rotating ring by a
tracking pattern that is not parallel to the raceway edges.
To prevent misalignment, shafts and housings should be checked for proper run-out of shoulders and bearing seats. Also use
single-point turned or ground threads on non-hardened shafts and ground threads only on hardened shafts. Precision
locknuts also can prevent misalignment.
Loose fits can cause relative motion between mating parts. Slight but continuous relative motion can lead to fretting of bearing
surfaces. If the looseness is sufficient to allow considerable movement of the outer or inner ring, the mounting surfaces (bore,
outer diameters, faces) will wear and overheat, causing noise and runout problems.
________________________________________
Keeping Bearings Clean
Follow these simple housekeeping rules when handling and installing bearings:
1. Work with clean tools in clean surroundings.
2. Remove all outside dirt from the housing before exposing bearings.
3. Handle with clean, dry hands.
4. Treat a used bearing as carefully as a new one.
5. Use clean solvents and flushing oils.
6. Lay bearings out on clean paper.
7. Protect disassembled bearings from dirt and moisture.
8. Use clean, lint-free rags if bearings are to be wiped.
9. Keep bearings wrapped in oil-proof paper when not in use.
10. Clean inside of housing before replacing bearings.
11. Install new bearings as removed from the package without washing.
12. Keep bearing lubricants clean when applying; cover containers when not in use.
Rolling-element bearings are highly precise components with internal tolerances on the order of millionths of an inch. So they
should be handled carefully to ensure that they perform as expected.
The critical factor in ensuring that a rolling element bearing reaches its expected life is cleanliness, before, during and after it
is installed. Cleanliness is important because once dirt or debris enters a bearing, it acts like an efficient lapping compound.
Even minute amounts of lint mixed with a lubricant can create an abrasive mixture.
Contaminants are generally miscellaneous particles that, when trapped inside a bearing, permanently indent rolling elements
and raceways under the tremendous pressure generated. Because of the relatively small contact area between rolling
elements and raceway, contact pressures are extremely high, even for lightly loaded bearings. When rolling elements roll over
contaminants, contact areas are greatly reduced, and pressure is extremely high.
When abrasive material contaminates the lubricant, it is crushed into fine particles that wear the rolling elements and
raceways. Therefore, it is important to maintain a clean environment when working on bearings. The assembly area should be
isolated from all sources of contamination, including moisture and corrosive elements. Workbenches, tools, clothing and hands
should be free of dirt, lint, dust and other contaminants that may harm the bearing. The work surface should be clean and
rubber coated if possible. Plastic coating is also a good idea. This helps avoid nicking spindle parts on hard surfaces and
allows the work surface to be wiped clean periodically. In addition, plastic and rubber coatings can be replaced easily and
economically.
Also, never remove a bearing from its carton before it is to be used because moisture and dirt can contaminate the bearing.
Bearings are wrapped in a special neutral, acid-free paper, and they should be rewrapped in such paper for storage. They
should never be stored unwrapped, and they should never be wrapped in plastic. Plastic traps moisture that can rust the
bearing.
Bearings shipped from the manufacturer are packed with a rust preventative to prevent corrosion. This rust preventative is
compatible with common oils and greases, and need not be removed prior to installation.
When personnel handle clean bearings, particularly the rolling surfaces of separable bearings, they should wear surgical
gloves. This prevents acid from the skin from leaving a deposit that can stain the bearing surface, leading to etching and
corrosion. If gloves are not available, hands should be clean and dry.
Cleanliness is important not only for bearings, but also for shafts and housings. Dirt on the shaft can be pushed to the
shoulder during bearing mounting, preventing proper seating and leading to possible fretting corrosion due to loose fits.
Proper Installation
Several studies have shown that poor handling, particularly during installation, accounts for a high percentage of bearing
failures. Depending on bearing type and size, mechanical, hydraulic or thermal methods are used for mounting. Regardless of
the mounting method, care must be taken to prevent bearing rings, cages and rolling elements from receiving direct blows,
and mounting force should not be directed through the rolling elements.
Mounting should preferably be done in a dry, dust-free room away from metalworking or other machines producing swarf and
dust. When a bearing must be mounted in an unprotected area, which is often the case for large bearings, steps should be
taken to protect the bearing and mounting position from contamination by dust, dirt and moisture until installation has been
completed. This can be done by covering or wrapping bearings and machine components with waxed paper or foil.
Foreign matter entering a bearing shortens life and causes one or all of the following operating conditions:
• Increased noise
• Increased friction
• Ball skidding
• Increased heat
• Reduced lubricant life
Bearings under four inches in diameter are usually cold press-fitted onto the rotating member. If the shaft rotates, press on the
inner ring; if the housing rotates, press on the outer ring. Pushing on the wrong ring forces the rolling elements to indent the
raceway, a condition called brinelling.
Bearings with large inner ring interference (and large bore bearings) require a considerable amount of force to mount at room
temperature. Heating to expand the inner ring eases assembly in these cases. The recommended method for heating up a
bearing for installation is an induction heater. A suitable induction heater will be equipped with a temperature sensor to attach
to the inner ring and a de-magnetization cycle.
Double-seal and double-shield bearings should not be heated above 250°F (120°C) to avoid damaging the seals or the
special grease they are packed with.
An induction heater is essentially a transformer that induces low-voltage, high-amperage energy into the bearing races,
resulting in quick, even heating. It is essential to apply heat uniformly throughout the entire bearing. Torches should never be
used to heat the inner ring during installation because they produce high localized heat that can damage bearing components
and the lubricant.
Pay special attention to the shaft condition when installing a bearing. Dirt or a burr on the shaft can create a stress riser that
can cause the bearing to fail quickly due to local overload.
Pillow block and flange bearings require some special attention to ensure that they are securely locked to the shaft. The most
widely used method of locking the inner ring to the shaft employs an inner ring with locking set screw. The preferred locking
mechanism for a mounted unit is a concentric locking sleeve.
Tapered bore ball bearings and spherical roller bearings can be mounted on a tapered shaft or with an adapter that has a
corresponding taper on the OD of the split sleeve.
During installation of tapered ball bearings, they should be tightened until there is a slight drag on the outer ring, then the
washer tang can be set. With spherical roller bearings, the unloaded side of each bearing should be measured and a
recommended amount of clearance removed before installation. Never mount a spherical roller bearing while the load is
applied to the bearing.
The inner ring of bearings with tapered bores is always mounted with an interference fit. The degree of interference is
determined by how far the bearing is driven onto the tapered seat on the shaft or onto the adapter or withdrawal sleeve. This
process reduces radial internal clearances. The amount of reduction provides information on the fit produced. Bearing
manufacturers publish guidelines on how much these clearances can be reduced without affecting performance.
Small bearings can be driven onto a tapered journal or withdrawal sleeve using a nut; they can be driven onto adapter sleeves
using the sleeve nut. A hook spanner or impact spanner can be used to tighten the nut. The seating surfaces of the shaft and
sleeve should be lightly oiled before mounting.
Larger bearings require considerably more force for mounting. Hydraulic nuts and oil injection equipment ease this process.
Misalignment and Loose Fits
Correct alignment is critical for bearings to operate properly. The misalignment capability of the bearing is determined by the
type and series of the bearing. Misalignment can cause an abnormal temperature rise in the bearing or housing and heavy
wear in the cage pockets of rolling elements. Misalignment can be detected on the raceway of the non-rotating ring by a
tracking pattern that is not parallel to the raceway edges.
To prevent misalignment, shafts and housings should be checked for proper run-out of shoulders and bearing seats. Also use
single-point turned or ground threads on non-hardened shafts and ground threads only on hardened shafts. Precision
locknuts also can prevent misalignment.
Loose fits can cause relative motion between mating parts. Slight but continuous relative motion can lead to fretting of bearing
surfaces. If the looseness is sufficient to allow considerable movement of the outer or inner ring, the mounting surfaces (bore,
outer diameters, faces) will wear and overheat, causing noise and runout problems.
________________________________________
Keeping Bearings Clean
Follow these simple housekeeping rules when handling and installing bearings:
1. Work with clean tools in clean surroundings.
2. Remove all outside dirt from the housing before exposing bearings.
3. Handle with clean, dry hands.
4. Treat a used bearing as carefully as a new one.
5. Use clean solvents and flushing oils.
6. Lay bearings out on clean paper.
7. Protect disassembled bearings from dirt and moisture.
8. Use clean, lint-free rags if bearings are to be wiped.
9. Keep bearings wrapped in oil-proof paper when not in use.
10. Clean inside of housing before replacing bearings.
11. Install new bearings as removed from the package without washing.
12. Keep bearing lubricants clean when applying; cover containers when not in use.
Official Government Bearing Supplier CAGE CODE: 5AX56
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