Editing Rolling-element bearing (section)

===Roller bearings===
[[File:Load Distribution Cylindrical Roller Bearing.gif|thumb|Load distribution (normal force per roller) in a cylindrical roller bearing of type NU206. The inner ring and rollers of the bearing rotate counterclockwise; a static radial load of 3,000 N acts on the inner ring in the downward direction. The bearing has 13 rollers, 4 of which are under load at all time.|256x256px]]

====Cylindrical roller====
[[File:Cylindrical-roller-bearing din5412-t1 type-n ex.png|thumb|left|100px|A cylindrical roller bearing]]

Roller bearings are the [[Bearing (mechanical)#History|earliest known]] type of rolling-element-bearing, dating back to at least 40 BC. Common roller bearings use cylinders of slightly greater length than diameter. Roller bearings typically have a higher radial load capacity than ball bearings, but a lower capacity and higher friction under axial loads. If the inner and outer races are misaligned, the bearing capacity often drops quickly compared to either a ball bearing or a spherical roller bearing.

As in all radial bearings, the outer load is continuously re-distributed among the rollers. Often fewer than half of the total number of rollers carry a significant portion of the load. The animation on the right shows how a static radial load is supported by the bearing rollers as the inner ring rotates.

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====Spherical roller====
[[File:Spherical-roller-bearing double-row din635-t2 120.png|left|thumb|100px|A spherical roller bearing]]
{{main|Spherical roller bearing}}

Spherical roller bearings have an outer race with an internal spherical shape. The rollers are thicker in the middle and thinner at the ends. Spherical roller bearings can thus accommodate both static and dynamic misalignment. However, spherical rollers are difficult to produce and thus expensive, and the bearings have higher friction than an ideal cylindrical or tapered roller bearing since there will be a certain amount of sliding between rolling elements and races.
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====Gear bearing====
[[File:Gear bearing view.jpg|left|thumb|100px|A gear bearing]]
{{Main|Gear bearing}}

Gear bearings are similar to [[epicyclic gearing]]. They consist of a number of smaller 'satellite' gears which revolve around the center of the bearing along a track on the outsides of the internal and satellite gears, and on the inside of the external gear. The downside to this bearing is manufacturing complexity.
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====Tapered roller====
[[File:Tapered-roller-bearing din720 120.png|thumb|left|100px|A tapered roller bearing]]
{{main|Tapered roller bearing}}

Tapered roller bearings use conical rollers that run on conical races. Most roller bearings only take radial or axial loads, but tapered roller bearings support both radial and axial loads, and generally can carry higher loads than ball bearings due to greater contact area. Tapered roller bearings are used, for example, as the wheel bearings of most wheeled land vehicles. The downsides to this bearing is that due to manufacturing complexities, tapered roller bearings are usually more expensive than ball bearings; and additionally under heavy loads the tapered roller is like a wedge and bearing loads tend to try to eject the roller; the force from the collar which keeps the roller in the bearing adds to bearing friction compared to ball bearings.
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====Needle roller====
[[File:Needle bearing.jpg|left|thumb|100px|A needle roller bearing]]
{{Main|Needle roller bearing}}

The needle roller bearing is a special type of roller bearing which uses long, thin cylindrical rollers resembling needles. Often the ends of the rollers taper to points, and these are used to keep the rollers captive, or they may be hemispherical and not captive but held by the shaft itself or a similar arrangement. Since the rollers are thin, the outside diameter of the bearing is only slightly larger than the hole in the middle. However, the small-diameter rollers must bend sharply where they contact the races, and thus the bearing [[Fatigue (material)|fatigues]] relatively quickly.
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==== CARB toroidal roller bearings ====
CARB bearings are toroidal roller bearings and similar to [[spherical roller bearing]]s, but can accommodate both angular misalignment and also axial displacement.<ref name="SKF, CARB" >{{cite web
 |title=CARB toroidal roller bearings 
 |publisher=[[SKF]]
 |url=http://www.skf.com/group/products/bearings-units-housings/roller-bearings/carb-toroidal-roller-bearings/index.html
}}</ref> Compared to a spherical roller bearing, their radius of curvature is longer than a spherical radius would be, making them an intermediate form between spherical and cylindrical rollers. Their limitation is that, like a cylindrical roller, they do not locate axially. CARB bearings are typically used in pairs with a locating bearing, such as a [[spherical roller bearing]].<ref name="SKF, CARB" /> This non-locating bearing can be an advantage, as it can be used to allow a shaft and a housing to undergo thermal expansion independently.

Toroidal roller bearings were introduced in 1995 by [[SKF]] as "CARB bearings".<ref name=":2">{{cite web|title=The CARB bearing – a better solution for the front side of drying cylinders|url=http://www.skf.com/files/519900.pdf|publisher=SKF|access-date=2 December 2013|url-status=dead|archive-url=https://web.archive.org/web/20131203011933/http://www.skf.com/files/519900.pdf|archive-date=3 December 2013}}</ref> The inventor behind the bearing was the engineer Magnus Kellström.<ref>{{cite web|title=CARB - a revolutionary concept|url=http://www.skf.com/binary/tcm:12-109023/6102_SV.pdf|publisher=SKF|access-date=2 December 2013}}</ref>