Understanding Spherical Plain Bearings (SPB)


Spherical Plain Bearings (SPB)/rod end bearings are generally used to connect or transfer movement such as connecting ends on control linkages, hydraulic cylinder rod ends, vehicle steering linkage suspensions, heavy equipment articulated joints and other severe duty uses where pivoting misalignment is present.

The challenge for the manufacturer is a balance of products to satisfy the vast array of application uses in the field. Especially when it comes to a customer’s cost control and budget needs.

Many off-the-shelf simple spherical plain bearings are constructed with an outer hardened ring made of bearing-grade steel and a precision-ground, hardened ball with a through bore. Other are more complicated in design to suit special function requirements. The SPB ball is electroplated – or coated – to prevent rust and help control wear while in service. Both component elements are formed into a single unit by the manufacturer. They can run dry, greased or have special lubricating liner or inserts added into the outer race and ball to make them maintenance-free.

Attention to application conditions is important when making the proper selection of SPB liner type and use. The SPB lubricating liners offered by suppliers include:

  • coatings,
  • oiled-filled pouros bronze,
  • plastics, metallic composites and
  • woven fabrics.

The latest innovation includes a composite steel back bronze PTFE material, such as CCTY’s TSA, which offers many improvements in lubrication even at low or elevated temperatures. Each liner offers specific strength, load capacity, temperature capability, frictional torque resistance and endurance life when used.

A better quality bearing can help achieve the best application results with a greater degree of design success, both in the short and long term. Without the manufacturers input, a low-quality SPB can actually harm equipment or damage end-product service integrity. In the worst case scenario, low-quality bearings can cause application to have problems in the field, resulting a costly replacement, service expense and warranty concerns.

Characteristics of good quality SPB bearings include:

  • High radial static load ratings
  • Good radial oscillating load ratings
  • High corrosion resistance
  • Maintenance-free characteristics
  • Long-term wear rate or bearing life
  • Broad operating temperature range
  • Multiple fluid compatibility
  • Contamination resistance
  • Ease of use in assemblies
  • Cost-effectiveness