Overcoming the energy thief known as friction has been going on for a long time. In 1493, Leonardo da Vinci documented the laws of sliding friction. Subsequently, several different individuals have contributed to an understanding of this natural force that resists motion and the continuous effort to overcome friction.
One technique used to accomplish this is the wheel. Evidence indicates that this rotating innovation appeared in Mesopotamia in the 3rd and 4th millennia B.C. Whatever the precise date, the wheel has been adapted to a plethora of applications since. From stainless steel roller bearings to gigantic Ferris wheels, the wheel is a mainstay of modern civilization.
An element of almost all modern wheeled devices is the use of bearings to distribute inherent forces and further improve efficiencies. Bearings are essentially wheels within wheels that allow independent rotation of the inside and outside elements known as races. These elegant devices come in two basic configurations. Ball bearings utilize spherical components while roller bearings use cylindrical elements. There are numerous subtypes of each.
Ball Bearing Types
Deep groove ball bearings are the most common and have inner and outer races with spherical metal balls captured between them. Some of this type include cages that hold the spherical balls captive within the races. The spheres are free to roll in all directions within the cage.
Angular contact ball bearings resemble deep groove types except for race surfaces that come in contact with the spheres having a specific angle. These angled races aid in transferring radial as well as axial forces more effectively.
Self-aligning ball bearings contain two rows of balls in the inner race and single row in the outer. This arrangement allows for a degree of freedom in the angle at which an axle can take relative to the inner race.
Thrust ball bearings accommodate forces perpendicular to the races. These are particularly useful when a drive shaft experiences force that acts in the axis perpendicular to the axis of rotation.
Roller Bearing Types
Spherical roller bearings use cylinders that include a radius in their profile. This feature allows some self-alignment as with the self-aligning ball bearings. These can also typically stand higher forces than ball bearings.
Cylindrical roller bearings substitute cylindrical-shaped roller elements for spherical. These are capable of withstanding much higher radial loads than other types.
Tapered roller bearings incorporate cylindrical rollers and races with a curved profile. As such, they are able to absorb and transfer much higher radial and axial forces.
Needle roller bearings include rolling elements that have a very small diameter. This type is only suited to radial forces.
Bearings provide an excellent method for reducing friction in rotating machinery. The variety of types permit their use in hundreds of different configurations. Overcoming resistance to the rotational movement of wheels is a key technique to increase efficiency.