Designs and variants
A characteristic feature of SKF steel/steel radial spherical plain bearings (table 1) is the outer ring, which is intentionally fractured so that it can be sprung apart to enable the inner ring to be inserted (fig. 1). Therefore, these bearings are non-separable and easy to handle.
The bearings are manganese phosphated and the sliding contact surface is then treated with a running-in lubricant. This reduces friction and wear during the running-in period. To facilitate lubrication, all bearings, with the exception of some small sizes, have an annular groove and two lubrication holes in both the inner and outer rings.
Heavy-duty spherical plain bearings have the SKF multi groove system in the outer ring sliding contact surface as standard (fig. 2). With the multi-groove system (fig. 3), SKF solved the problem of lubricant starvation in steel/steel bearings. Lubricant starvation is a common cause of premature bearing failure in applications where minor alignment movements are made under heavy, constant direction loads.
The multi-groove system improves lubricant distribution in the heavily loaded zone to extend bearing service life and/or maintenance intervals.
Bearings and rod ends requiring maintenance must be greased prior to being put into operation. With the exception of a few applications, they must be relubricated periodically.
SKF Explorer steel/steel radial plain bearings (table 2) are virtually maintenance-free (Bearing designs and features - SKF Explorer steel/steel plain bearings). The sliding surfaces are treated further to improve wear and corrosion resistance. All series have an outer ring that is intentionally fractured to allow for the inner ring to be inserted. The bearings are non-separable.
SKF manufactures maintenance-free radial spherical plain bearings in a variety of designs and a wide range of sizes. Three sliding contact surface combinations are available:
- steel/PTFE sintered bronze, designation suffix C (table 3)
- steel/PTFE fabric, designation suffix TX (table 4)
- steel/PTFE FRP, designation suffix F (table 5)
All three sliding contact surface combinations are self-lubricating. Bearings with a steel/PTFE sintered bronze or steel/PTFE fabric sliding contact surface combinations must not be lubricated. Bearings with a steel/PTFE FRP (fibre reinforced polymer) sliding contact surface combination are also maintenance-free, whereas occasional relubrication is beneficial to help maximize bearing service life. To facilitate relubrication, steel/PTFE FRP bearings are equipped with lubrication facilities.
Table 6 provides an overview of the different design features. They depend on the size and series, with the main differences being the material or the design of the outer ring.