Radial ball joints incorporate two distinct structural elements:
- Inner ring with spherical and convex outer surface
- Outer ring with spherical and concave inner surface
The complementary curvatures make them particularly suitable for bearing arrangements where alignment movements between the shaft and housing must be taken into account, as well as where oscillatory or recurrent tilting or rotation movements occur at slow sliding speeds.
Bearings are available in two main variations: maintenance-requiring spherical plain bearings (steel-on-steel) and maintenance-free spherical plain bearings. The first requires regular lubrication and is suitable for heavy loads moving in alternating directions; and the latter has low friction and is used for applications where long bearing life is required or where operating conditions make steel-on-steel bearings impractical.
Maintenance for both differs and reflects their composition. For maintenance-type spherical plain bearings, some bearing designs can be equipped with seals to repel contamination, while many split outer rings can be equipped with retaining rings. Spacers and extended inner rings can also be incorporated.
For maintenance-free type plain bearings, the carbon steel outer rings may be pressed around the inner ring or may have radial slots joined by screws. Some models may be equipped with seals that prevent contaminants from entering. Some may also be equipped with retaining rings.
An important note for both concerns the operating temperature range. Radial plain bearings made of steel-on-steel fabric, steel-on-PTFE and steel-on-PTFE fabric can be used at temperatures between -50° C and +150° C, while spherical plain bearings with seals can be used at temperatures of –30° C to +130° C. Higher temperatures reduce its load capacity
