In an unmounted bearing, the space between the rolling elements and the races.

Radial clearance is needed because the press fit of a shaft through a bearing's inner race will cause it to enlarge and/or the press fit of the outer race in a housing will make it slightly smaller. Radial clearances are designed such that the assembled, operating bearing has the desired net clearances, not running too loose or too tight.

Roller Bearing Manufacturing Engineering Committee

Generally, any metal with a melting point above the range for iron, cobalt and nickel. Examples are tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and rhenium.

Also known as a Cage.

The device used to space, separate and retain the balls or rollers of a rolling element bearing. Retainers are most often constructed from steel, plastic or brass.

Bearing manufacturer acquired by NSK in 1990.

RHP was created by an early 1970s merger of three British bearing manufacturers, taking its name from the three: Ransome & Marles Bearing Company, Hoffman Manufacturing Company, and Pollard Ball & Roller Bearing Manufacturing.

A series of reference standards for measuring material hardness.

A Rockwell hardness measurement is calculated from the depth of the indentation caused by a standardized steel ball or diamond cone applied under constant load. For best results, the material being tested should be flat.

There are several Rockwell scales, but A, B and C are the most popular. They refer to the different materials being tested, testers and force applied.
A : for extremely hard materials
B : for medium hardness materials, annealed low-carbon and medium-carbon steel
C : for materials greater than 100 on the Rockwell B scale

In the bearing industry, the most commonly used Rockwell hardness scale is the C scale, often shortened to Rc. The Rc scale is measured by applying a 120-degree-angle pyramid-shaped diamond cone under a constant 150kg load. Results will be in the range of Rc 20 to Rc 70.


Related publication link:
Rockwell Hardness Measurement of Metallic Materials
NIST Recommended Practice Guide
Special Publication 960-5
[2001; 118 pages; PDF file]

Any bearing where the relative motion of two surfaces is separated by balls or rollers as the friction-reducing component.

Rolling element bearings consist of several parts - most have an inner race, an outer race, rolling elements in between, and a retainer or cage to separate and position the rolling elements. At minimum, a rolling element bearing can be an outer race the rolling elements - held in place by snap rings or formed portions of the outer race. Retainers or cages are also optional, and must be deleted to build a full-complement bearing.

The study of rotating machines.

The general study of rotor dynamics is broken down into several separate disciplines: bearings, shafts, seals, stability/instability, balance/out of balance, and condition monitoring.

A type of bearing where the two surfaces come in contact or rub together.

An unlubricated bushing is an example of a rubbing bearing. Rubbing bearings are most often made of or coated with materials with inherent lubricity, such as carbon, polytetraflouroethylene (PTFE), or various plastics.