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A ball bearing is a common type of rolling-element bearing, a kind of bearing.

The term ball bearing to mechanical engineers usually means a bearing assembly which uses spherical bearing balls as the rolling elements. To laypeople the term often means an individual ball for a bearing assembly. The remainder of this entry uses the term ball for the individual component and "ball bearing" or just "bearing" for the assembly.

Ball bearings typically support both axial and radial loads and can tolerate some misalignment of the inner and outer races. Also, balls are relatively easy to make cheaply compared to other kinds of rolling elements. Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area that spherical shapes provide.

Although Leonardo da Vinci has been credited with the discovery of the principle behind the mechanics of ball bearings, the first patent was taken out by Philip Vaughn, a Welsh carriage-maker, in 1791, and ball bearings were found on the Roman Nemi ships constructed in about 40 A.D..

Contents 1 Common designs 1.1 Radial 1.2 Angular contact 1.3 Axial 1.4 Deep-groove 2 Construction types 2.1 Conrad 2.2 Slot-fill 2.3 Split-race 2.4 Single-row versus double-row 2.5 Caged 2.6 Ceramic hybrid ball bearings using ceramic balls 3 Trivia 4 See also 5 References 6 External links

There are several common designs of ball bearings, each offering various tradeoffs.

A radial ball bearing uses axially symmetric inner and outer races that are shaped so a radial load passes radially through the bearing. Most radial designs also support modest axial loads; however, large axial loading tends to separate the bearings.

An angular contact ball bearing uses axially asymmetric races. An angular load passes in a straight line through the bearing, whereas a radial load takes an oblique path that tends 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 allow '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. The angular-contact bearing is able to withstand such a combined load, as well as small misalignments which often occurs, due to the flexibility of the front fork.

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.

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.

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 being used in most of the mechanical Industries

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.

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.

Most ball bearings are single-row designs. Some double-row designs are available but they need better alignment than single-row bearings.

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.^[1]

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.

Trivia sections are discouraged under Wikipedia guidelines. The article could be improved by integrating relevant items and removing inappropriate ones.

• 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.^[2]

• Ball screw
• Bearing (mechanical)
• Linear bearing
• Rolling-element bearing
• Brinell scale, a material hardness scale that can help determine the failure mode of ball bearings
• SKF (Svenska Kullagerfabriken), ball bearing manufacturer founded by Sven Wingquist
• Schaeffler Group, ball bearing manufacturer
• Thrust bearing
• ZNL Bearing, ball bearing manufacturer

• SKATE Bearings
• Animated 3D-model of ball bearing, explaining rotation, can be viewed in most browsers
• Various 3D CAD models and 2D CAD drawings from various manufacturers can be downloaded from 3D ContentCentral for use in all major CAD systems
• Pacific Bearing (a manufacturer of linear motion bearings and linear plain bearings)
• igus plastic ball bearings
• Technical data for radial ball bearings