The image above shows several ball bearing types.
A ball bearing is a mechanical assembly that carries loads, reduces friction, supports positioning, and facilitates rotational and/or oscillatory motion. It is more than just than just a single BB-shaped ball. Ball bearings can be manufactured with a higher or lower level of precision and are used in a variety of applications. Precision bearings are required by the aerospace, military and defense, medical, and semiconductor industries.
The Parts of a Ball Bearing
A ball bearing contains these parts.
- two races (inner and outer)
- multiple spherical rolling elements
- a retainer/cage, or filling slots for full complement ball bearings
Inner vs. Outer Races
Ball bearings have two ring-shaped races, or raceways, that hold the individual balls and transmit loads through them. These races provide a fixed path on which balls can roll and glide while generating little friction. Each race has a grooved surface, and some are grooved more deeply than others. The outer race contacts the outside of the balls, the inner race contacts the inside of the balls, and the balls remain between these two races.
The Balls in a Ball Bearing
Balls can be made of stainless steel, glass, acetal, ceramic, or polypropylene. In addition, the balls and races can be made of the same material or different materials. Typically, precision bearings for aerospace, aircraft and aviation use SAE 52100, 440C or 440C modified steel, CREN high nitrogen stainless steel, or M50. Hybrid bearings with ceramic elements for higher speeds and extended wear life are also used in demanding applications.
The Retainer or Cage
A ball bearing retainer (also called a cage) is a separator that maintains the balls’ radial spacing from each other. Retainers can also provide lubrication by serving as a reservoir for oils or supplying a solid film. There are several common types of cages, including special cages for aircraft bearings. Prior to assembly, the retainers are cleaned carefully and then lubricated. With some precision bearings, military-grade greases are required.
Ball Bearing Specifications and Types
In addition to materials of construction, ball bearings are specified by dimensions, rated speed, dynamic axial load, and dynamic radial load. Bore diameter, outside diameter, cross section and overall width are key dimensional specifications. With standard ball bearings, the cross section increases in proportion to the bore diameter. With thin section bearings, however, the cross-section dimension does not. In other words, the cross-section size remains the same even when the bore diameter increases.
There are many different types of ball bearings, including various subtypes. The following is a partial list with some brief definitions and use cases.
Angular Contact Bearings
Angular contact ball bearings have inner and outer raceways that are displaced relative to each other in the direction of the bearing axis. This enables them to accommodate combined radial and axial loads.
- Single row angular contact bearings have one row of balls.
- Double row angular contact bearings have two rows of balls.
- Four-point angular contact bearings support axial loads in all directions
Deep Groove Bearings
Deep groove ball bearings can support heavy loads while offering both axial and radial support. The term “groove” refers to the depth of the raceway into which the balls fit.
- Single row deep groove ball bearings have low torque and support high speeds.
- Double row deep groove ball bearings have a higher load-carrying capacity and full shoulders on the sides of the raceways to support the addition of shields or seals.
Precision Ball Bearings
Precision ball bearings include both angular contact bearings and deep groove bearings. Therefore, the definition of a precision bearing involves manufacturing. A ball bearing’s ABEC rating describes the level of manufacturing tolerances, or acceptable part-to-part variations. Bearings with lower ABEC ratings are less precise and bearings with higher ABEC ratings are more precise.
Ball bearings with precision levels less than ABEC 1 are considered to be unground bearings. Applications include ceiling fans, hoists, and trailer jacks – just to name a few. Semi-ground bearings are also available, but precision bearings meet at least ABEC level 3 . Precision bearings are more challenging to produce, but they support high accuracy, high rigidity, and high speeds.
Full Complement Bearings
Full complement bearings don’t have a cage. Instead, both rings have filling slots to allow the maximum number of balls to be installed in the bearings. This results in a much higher load-carrying capacity, but there are tradeoffs. For example, full complement bearings are used only in applications that have radial loads. In other words, they can’t support thrust or moment loads. Typically, full complement bearings are used in slower speed applications.
Finding a Ball Bearing Supplier
Schatz Bearing is ball bearing supplier that designs and manufactures products in an ISO 9001:2015 and AS9100 Rev. D certified facility in Poughkeepsie, New York (USA). We are also ITAR registered and can supply you with bearings that meet Boeing standards or MIL-SPEC standards.
Do you need a ball bearing that is an unground, semi-ground, or high precision product? Contact Schatz.
