what is Ball bearing
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.
There are several common designs of ball bearings, each offering various tradeoffs.
Radial
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.
Angular contact
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 fork.
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..
Construction types
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 being used in most of the mechanical industries.
Relationship Bearing News
1. NH Ball Bearings' Astro Division recognized by Northrop Grumman
2. Angular Contact Ball Bearing
