What Is a Spherical Plain Bearing? Structure, Types & How It Works

A spherical plain bearing is a sliding bearing built around matching spherical surfaces. The inner ring has a convex outside surface and the outer ring has a concave inside surface, so the joint can carry load while accommodating angular movement that would be difficult for a rigid cylindrical bushing.

What is a spherical plain bearing?

Unlike a ball or roller bearing, a spherical plain bearing does not use rolling elements between two raceways. Load is transmitted through a broad sliding contact. That makes the product especially useful in slowly oscillating pivots, reversing linkages, clevis joints and articulated mechanisms where shaft alignment changes during motion.

Key components

• Inner ring: the bore fits the pin or shaft, while the outer surface forms the convex spherical sliding face.
• Outer ring: the outside diameter fits the housing; its inside surface forms the mating concave sphere.
• Sliding system: depending on series, the interface may be steel/steel, steel/PTFE composite, steel/PTFE fabric or steel/bronze.
• Lubrication or liner: greaseable series rely on a planned relubrication path, while lined maintenance-free designs use the liner as the sliding system.

Main types in the EVER POWER range

How the joint works

When the connected parts articulate, the inner ring rotates or oscillates relative to the outer ring while the spherical surfaces remain in contact. The permitted articulation depends on the exact model geometry. Load then passes from the pin through the inner ring, across the spherical sliding interface, into the outer ring and finally into the housing.

Common applications

Typical uses include hydraulic-cylinder eyes, agricultural linkages, excavator boom and bucket pivots, railway linkages, marine steering joints and selected automation mechanisms. The same bore size can appear in very different series, so the application, maintenance route and contamination level matter as much as the nominal diameter.

Reading a part number

Take EP-GE20ES as an example. The EP- prefix identifies the EVER POWER catalogue identity, GE identifies the radial family, and 20 is the nominal 20 mm bore. Suffixes such as ES, 2RS, C or ET describe construction details such as lubrication features, sealing or liner type. Always confirm the full suffix rather than ordering from the bore number alone.

How it differs from a plain cylindrical bushing

A cylindrical bushing can support a pin with sliding contact, but it does not intentionally provide the same spherical articulation. If the linkage changes angle because of frame deflection, manufacturing tolerance or mechanism motion, a spherical plain bearing can accommodate that angular relationship inside the bearing instead of forcing the pin to bend or the bushing edge to carry the load. That distinction is one reason spherical plain bearings are common at clevises and articulated connections.

What to measure before ordering

• Measure the pin or shaft diameter to establish the nominal bore d.
• Measure the housing bore and available width, then compare D, B and C with the model table.
• Record the maximum articulation through the complete machine cycle, not only at the neutral position.
• Decide whether the joint has a reliable grease route or needs a maintenance-free liner.
• Describe dust, water, wash-down, salt, chemicals or other contamination that can reach the bearing faces.

A useful way to think about series choice

The family code is a compressed description of construction. GE is the compact general radial route, GEG is the wider heavy-duty route, C and ET identify maintenance-free liner systems, and 2RS identifies face sealing. The model number then narrows the size. That means a buyer should first choose the construction logic, then check the exact size. Reversing those steps can lead to a 20 mm bore bearing that physically fits the pin but does not match the housing, maintenance plan or environment.