four-point contact ball bearing can accommodate axial loads in both directions, in combination with radial loads up to a certain level, and provides a very tight axial shaft position tolerance. The bearing also saves space, because it can be seen as the combination of two single row angular contact ball bearings into one. Therefore, it is an excellent choice in applications such as industrial gearboxes, locomotive drives and compressors.
Standard four-point contact ball bearings consist of a single piece outer ring, a radially split inner ring, a ball set and an outer ring guided cage. The ring designs show some remarkable details The outer ring is similar to a deep groove ball bearing design, but the raceway geometry cross section is fairly different. A deep groove ball bearing raceway is circular. A four-point contact ball bearing outer ring consists of two symmetrical raceways. Each of them has a circular shape. The two raceways intersect each other in the middle of the ring in form of a singular point. The raceways form is also called “Gothic arc.” The centers of the two raceway circles have a small off-set in axial direction .The inner ring is split into two halves and has the same design principle as the outer ring. This provides an advantage compared to the deep groove ball bearing design. The design of the outer ring raceways allows defining the contact angle (standard 35°) and the axial clearance independently. In other words it is possible to design a specific axial clearance without changing the osculation (ratio between raceway curvature and ball diameter).
A bearing with a 35° contact angle requires high raceway shoulders and such a bearing with a single piece inner ring cannot be assembled with a reasonable number of balls. The four-point contact ball bearing split inner ring design makes it possible to incorporate a maximum number of balls, only limited by the cage bar thickness.
Typically, there is a three-step assembly procedure:
the cage is inserted in the outer ring,
the balls are pressed into the cage,
the inner ring halves are inserted from each side. The inner rings are not self-retaining. To avoid the bearing falling apart during transport and handling, a plastic insert is pushed into the bore.
Applications
If the design space is limited, heavy axial loads in both directions occur or speeds are high, four-point contact ball bearings are worth considering. Such conditions might occur in applications such as pumps, retarders, compressors, industrial or automotive gearboxes, traction motors or steering columns