BEARINGS - ThomasNetRoller bearings employ a host of different shapes for their rolling elements, including straight rollers, needle rollers, tapered rollers, spherical rollers, etc.

BEARINGSBUYING GUIDE

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BEARINGS A ThomasNet Buying Guide

Bearings are mechanical assemblies that consist of

rolling elements and usually inner and outer races

which are used for rotating or linear shaft

applications. There are several different types

including ball and roller bearings, linear bearings, as

well as mounted versions that may use either rolling

element bearings or plain bearings. Ball bearings have

spherical rolling elements and are used for lower load

applications, while roller bearings use cylindrical rolling elements for heavier load carrying

requirements. Linear bearings are used for linear movements along shafts and may also have rotational

capabilities. Mounted bearings are assemblies in which the bearings are pre-assembled in mountings

that, in turn, are bolted to frames, stanchions, etc., and are used for supporting the ends of shafts,

conveyor rollers, etc. In addition to ball and roller bearings in their radial, linear, and mounted forms,

bearings include those for civil engineering applications, which are called slide bearings; those used in

small instruments and the like, known as jewel bearings; and very specialized bearings known

collectively as frictionless bearings which includes air and magnetic varieties. Sleeve bearings, journal

bearings, and other fluid-film bearings are addressed in the Bushings family.

Types of Bearings

Ball Bearings Ball Bearings are mechanical assemblies that consist of rolling spherical elements

that are captured between circular inner and outer races. They provide a means

of supporting rotating shafts and minimizing friction between shafts and

stationary machine members. Ball bearings are used primarily in machinery that

have shafts requiring support for low friction rotation. There are several

configurations, most notably shielded or sealed. Ball bearings are standardized to

permit interchangeability. Ball bearings are also known as rolling element

bearings or anti-friction bearings. Considerations include

First choice for high speeds or high precision apps

Large range of standardized forms

Handle radial and axial loads with specific configurations

Roller Bearings Roller Bearings are mechanical assemblies that consist of cylindrical or

tapered rolling elements usually captured between inner and outer races.

They provide a means of supporting rotating shafts and minimizing

friction between shafts and stationary machine members. Roller bearings

are used primarily in machinery with rotating shafts that require support

of heavier loads than ball bearings provide. Tapered roller bearings are

often used to accommodate higher thrust loads in addition to the radial

loads. Types range from cylindrical to spherical rollers. Roller bearings are

standardized like ball bearings, albeit to a lesser degree. Considerations

include

Higher load capacities than ball bearings

Can withstand high axial loads

Mounted Bearings Mounted Bearings are mechanical assemblies that consist of bearings

housed within bolt-on or threaded mounting components and

include pillow blocks, flanged units, etc. They provide means of

supporting rotating shafts and minimizing friction between shafts

and stationary machine members. Mounted bearings are used

primarily in machinery with exposed rotating shafting. They are used

as take-up devices on the ends of conveyors and as flanged units

along intermediate points. The bearings can be rolling element or

journal bearing configurations. Mounted bearings are designed for

bolt-on mounting and ease of replacement. Other varieties of

mounted bearings include rod end bearings and cam followers.

Considerations include

Housed units reduce mounting concerns, protection issues

Cartridge designs ease replacement

Shafts usually held in place with set screws

Allow adjustment of the supported components

Mainly used for low/mid speed applications

Linear Bearings Linear Bearings are mechanical assemblies that consist of ball or roller

elements captured in housings and used to provide linear movement

along shafts. Linear bearings are used primarily in machinery that requires

linear movement and positioning along shafts. They also may have

secondary rotational features depending on the design. Considerations include

Lower friction and higher accuracies compared with bushings

Costlier and more complex than bushings

Slide Bearings Slide bearings are mechanical assemblies designed to provide free

motion in one dimension between structural elements. Slide bearings

are used primarily in the structural support of bridges as well as

commercial and industrial buildings. These parts accommodate

thermal movement, allow for end-beam rotation, and isolate

components of the structure against vibration, noise, and shock.

Other types of slide bearings include those used on truss base plates, heat exchangers, and process

equipment.

Jewel Bearings Jewel bearings are mechanical devices used in

light rotating applications such as watches, meter

movements, gyroscopes, etc. where loads are

small and the supported rotating shafts are tiny.

Jewel bearings are constructed from a range of

synthetics, with ruby and sapphire being

particularly common.

Frictionless Bearings Frictionless bearings are mechanical or electro-mechanical alternatives to

conventional bearings that provide controllable shaft support through air,

magnetic fields, etc. for critical, high precision applications.

Applications and Industries Ball and roller bearings are used in machinery of all kinds, from boiler feed pumps to automotive

transmissions. Mounted bearings are especially common on conveyors, in shaft linkages, and

particularly where long lengths of shafting must be supported by housed units where the bearing is not

protected by another housing such as a transmission case. Linear bearings are used exclusively in linear

applications such as slide tables. Slide bearings are used primarily for load bearing application in large

civil engineering projects such as bridges where they accommodate a limited range of movement, unlike

the other bearings here, where motion—either radial or linear—is the main concern. Jewel bearings are

restricted to very small devices and movements and do not rely on any rolling elements. Frictionless

bearings are any of the other special purpose designs that include air bearings, magnetic bearings, etc.

While bearings are used nearly everywhere, there are some industries that use so many or have specific

requirements for durability, cleanliness, etc. that they warrant mentioning here. Some of these

industries are

Aerospace

Agricultural

Automotive

Machine Tools

Medical

Mining

Considerations Radial ball bearings are used primarily for radially loaded shafts and those with light axial loads. Angular

contact ball bearings are designed to take higher axial loads in one direction in addition to their radial

capacities. Ball thrust bearings are available which are specifically intended to take axial loads alone. The

most common configuration for radial ball bearings is the single row version, which could be shielded or

sealed depending on whether it is to be used within a housed area—a transmission, say—or in an

exposed environment such as on a bicycle wheel. The seals and shields keep lubricant in the bearing and

dirt and debris out of it. Ball bearings are usually fitted with retainers which space the balls evenly

between and around the perimeters of their outer and inner races. Full capacity bearings dispense with

retainers in order to fill as many balls as possible between the races, adding to the bearing’s load

handling capacity.

Roller bearings employ a host of different shapes for their rolling elements, including straight rollers,

needle rollers, tapered rollers, spherical rollers, etc. Roller bearings are able to take higher radial loads

than their ball bearing counterparts due to the higher contact area between the rollers and the races.

Some roller bearings are designed to take high thrust loads using tapered elements and races.

Mounted bearings are ball, roller, or sleeve bearings which are furnished in housings, flanges, etc. and

usually installed with seals and/or shields for environmental protection. Common mounting styles

include pillow blocks, flanges, take-ups, etc. They are often used on conveyors where take-up

assemblies provide adjustment for conveyor belt tension.

In selecting rolling element bearings, either ball or roller or as mounted units, designers usually consider

a number of factors including loads, both their quantities and directions, the accuracy requirements of

the shaft system, misalignment factors, speeds, noise, and friction. Where radial loads are high, a

designer may opt for a roller bearing over a ball bearing and might do the same where high axial loads

are anticipated. Where the bearing needs to be able to accommodate some shaft misalignment, the

designer may elect a ball bearing where loads are normal or go to a spherical roller bearing which is also

very capable of handling misalignment. Ball bearings tend to be better at handling high speeds than

roller bearings, and in some cases where accuracy and low friction are paramount, such as machine

tools, a ball bearing may be the only way of meeting the requirements.

Of particular interest in considering bearings are their static and dynamic load ratings. Bearing that are

subject to high loads when they are not rotating can undergo a phenomenon known as brinelling, where

the balls dent the races in the same place repeatedly. The same loads applied to the bearing when

running may cause less concern because any indentations will distribute around the bearing races and

not pile up in the same spots each time.

Bearing makers list bearing rated capacities for their bearings, which for ball bearings are identified as

extra-light, light-, medium-duty, and so on, where the dimensions of the bore or shaft requirements

increase to accommodate increasing loads. The rated capacity is based on a statistical measure which

states that a certain percentage of bearings will complete a stated number of revolutions without failing.

These catalog numbers can be massaged to better pick the bearing suited to the actual conditions of

use.

Linear bearings are sized according to linear travel, total linear distance, load, precision requirements,

etc., with many parameters being analogous to the radial bearing considerations. Linear bearings are

used with ground shafting for dimensional accuracy and low-friction sliding.

Slide bearings are used to accommodate expansion and contraction in stationary structures such as

bridges and building. Often they consist of two Teflon plates which are sandwich between major

structural members. Sometimes stainless steel is used instead of Teflon for one of the two facing

bearing surfaces. Of principal concern with slide bearings is the force per unit area they can withstand.

Jewel bearings are used in very light loading applications. Jewel bearings provide very accurate, hard

surfaces which can support lightly loaded shafts that see mostly intermittent motion.

Frictionless bearings are bearings that use air or other gases or magnetic fields to support rotating

journals and are so-called to distinguish them from anti-friction bearings—another term for rolling

element bearings, which in itself was coined to distinguish these from original journal bearings which

used friction developed through shaft rotation to create films of fluid for supporting shaft journals.

Frictionless bearings represent a small slice of the bearing world and are usually applied only in very rare

situations.

ABMA The ABMA (American Bearings Manufacturers Association) provides standards for many bearing types

and is affiliated with the so-called ABEC system which rates bearing precision.

Important Attributes

Bearing Type For ball bearings, the Conrad, or non-slot fill, bearing is the most common, whose design dispenses with

a filling slot and instead relies on displacing the inner race to load the balls and a cage to keep them

evenly spaced. For roller bearings, bearing type requires a selection of roller type, be it cylindrical,

tapered, spherical, etc. Mounted units require a type selection of ball, roller, or spherical, as well, and

then an additional selection of style, as defined below. Linear bearing types range from ball bearing

cages—essentially bare cages holding balls that are often used as die-post bushings—to recirculating

ball designs where the balls roll linearly along the shaft and then return to their starting points through

channels on the non-shaft sides of the bearings.

Style This attribute applies solely to mounted units, where a distinction must be made between the housing

for the bearing, among them the choice of pillow blocks, flanges, take ups, etc.

Material Material choice for ball and roller bearings is generally limited to a few steel alloys, some plastics,

occasionally ceramics, etc. while mounted units have more material choices owing to the additional

materials available for housings.

Seal/Shield Ball bearings exposed to the environment can be ordered with seals and/or shields

where shields provide some protection of the bearing elements from dirt ingress with

minimal added friction and seals provide shaft contacting lips that exclude moisture but

do add to the friction on the bearing. Seals and shields can be added on both sides,

either side, alone or in combination. The image to the right shows a radial bearing in

cross section with shields on both sides.

Race Ball bearings races fall generally into two designs: angular contact and radial. Angular

contact bearings (image right) load the balls at angles to the perpendicular radial

planes, whereas radial contact bearings (image above) load the balls through the

perpendicular planes. Angular contact bearings are generally preferred where axial

loading is a consideration. Deep groove bearings are commonly associated with

radial contact bearings. Cup and cone bearings are common on bicycle wheels where the bearings are

loosely packed between cones and the cones are adjusted for play.

Locating Mounted pillow block units are classified as expandable and non-expandable and in situations where

two are more pillow block bearings are installed for shaft support one will ordinarily be specified as non-

expandable and the other as expandable which allows the bearing to accommodate slight growth of the

shaft. Some units are configured to allow either option.

Maximum Static and Dynamic Loads Bearing loading is based on static and dynamic values and the choice of which governs is a function of

the operating conditions the bearing will see.

Related Product Categories Shafts (Shafting) are mechanical components, usually metallic, that typically rotate axially to

transmit motion.

Hydraulic/Pneumatic/Radial Shaft Seals are mechanical devices used for sealing the

components of reciprocating and rotating shafts where fluid is used as an actuating force or

where oil/grease are used as lubricants.

Lubricating Greases are semi-solid mixtures of lubricants and thickeners usually made from

minerals and soaps to produce a higher viscosity than oil and used to prevent wear on contact

surfaces.

Lubricating Oil is a slippery and viscous liquid made of any of numerous mineral, vegetable,

animal, or synthetic substances. It is often a mixture of gaseous, liquid, and solid hydrocarbons

used for lubricating. It is also available in synthetic and edible forms.

Plain Bearings (Bushings) are mechanical elements used to reduce friction between rotating

shafts and stationary support members. Typically, a bushing relies on soft metal or plastic and

an oil film to support the rotating shaft on the hardened shaft journal.

Bearing Isolators are mechanical devices designed to seal and protect bearings from infiltration

by fluid and airborne contaminants.

Chain and Bearing Lubricators are mechanical devices used to deliver oils, grease, or other

lubricants to moving or contacting parts or joints for the purpose of reducing friction.

Induction Heaters are devices that use electromagnetic energy to induce heating in electrically

conductive materials. Heaters are sometimes used for bearing installation.

Resources

General Ball Bearings http://www.timken.com/en-us/products/bearings/productlist/ball/Pages/default.aspx Needle Bearings http://www.ntnamericas.com/en/website/documents/brochures-and-literature/tech-sheets-and-supplements/needle_roller_bearings_handbook_cat_9013-e_lowres.pdf Mounted Units http://www.ktntn.com/pdfs/Introduction%20to%20Mounted%20Unit%20Bearings.pdf Linear Bearings http://www.bsahome.org/tools/pdfs/Linear_Bearings_web.pdf Trade Associations http://www.americanbearings.org/ http://www.bsahome.org/default.aspx

Manufacturers and Suppliers http://www.intechbearing.com/ http://www.spb-usa.com/ http://www.tpa-us.com/index.html http://www.emersonbearing.com/index.html http://www.kmsbearings.com/ http://www.nomabearing.com/index.html http://www.timken.com/en-US/Pages/Home.aspx